VANGUARD WORLD FUND INC
485APOS, 2000-02-23
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                       SECURITIES AND EXCHANGE COMMISSION
                             WASHINGTON, D.C. 20549


                                    FORM N-1A

      REGISTRATION STATEMENT (NO. 2-17620) UNDER THE SECURITIES ACT OF 1933


                           PRE-EFFECTIVE AMENDMENT NO.
                         POST-EFFECTIVE AMENDMENT NO. 78


                                       AND

         REGISTRATION STATEMENT UNDER THE INVESTMENT COMPANY ACT OF 1940


                                AMENDMENT NO. 78




                              VANGUARD WORLD FUNDS
         (EXACT NAME OF REGISTRANT AS SPECIFIED IN DECLARATION OF TRUST)

                      P.O. BOX 2600, VALLEY FORGE, PA 19482
                     (ADDRESS OF PRINCIPAL EXECUTIVE OFFICE)

                  REGISTRANT'S TELEPHONE NUMBER (610) 669-1000

                           R. GREGORY BARTON, ESQUIRE
                                  P.O. BOX 876
                             VALLEY FORGE, PA 19482


                IT IS PROPOSED THAT THIS FILING BECOME EFFECTIVE:
            ON APRIL 28, 2000, PURSUANT TO PARAGRAPH (A) OF RULE 485.


                  APPROXIMATE DATE OF PROPOSED PUBLIC OFFERING:
   AS SOON AS PRACTICABLE AFTER THIS REGISTRATION STATEMENT BECOMES EFFECTIVE.






<PAGE>
SUBJECT TO COMPLETION
PRELIMINARY PROSPECTUS
DATED FEBRUARY 23, 2000

VANGUARD(R) CALVERT SOCIAL INDEX FUND
PROSPECTUS
APRIL 28, 2000

This is the Fund's initial
prospectus, so it contains
no performance data.

INFORMATION   CONTAINED  HEREIN  IS  SUBJECT  TO  COMPLETION  OR  AMENDMENT.   A
REGISTRATION STATEMENT RELATING TO THESE SECURITIES HAS BEEN FILED WITH THE U.S.
SECURITIES AND EXCHANGE  COMMISSION BUT HAS NOT YET BECOME EFFECTIVE.  SHARES OF
VANGUARD  CALVERT  SOCIAL  INDEX FUND MAY NOT BE SOLD,  NOR MAY OFFERS TO BUY BE
ACCEPTED,  PRIOR TO THE TIME THE REGISTRATION STATEMENT BECOMES EFFECTIVE.  THIS
COMMUNICATION  SHALL NOT  CONSTITUTE  AN OFFER TO SELL OR A  SOLICITATION  OF AN
OFFER TO BUY,  NOR  SHALL  THERE BE ANY SALE OF THESE  SECURITIES  IN A STATE IN
WHICH SUCH OFFER, SOLICITATION,  OR SALE WOULD BE UNLAWFUL PRIOR TO REGISTRATION
OR QUALIFICATION UNDER THE SECURITIES LAW OF THE STATE.

[A MEMBER OF
THE VANGUARD GROUP LOGO]

<PAGE>

VANGUARD CALVERT SOCIAL INDEX FUND
Prospectus
April 28, 2000

A Stock Index Mutual Fund


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CONTENTS
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 . FUND PROFILE                          . SHARE PRICE
 . ADDITIONAL INFORMATION                . INVESTING WITH VANGUARD
 . AN INTRODUCTION TO INDEX FUNDS        . SERVICES AND ACCOUNT FEATURES
 . A WORD ABOUT RISK                     . TYPES OF ACCOUNTS
 . WHO SHOULD INVEST                     . BUYING SHARES
 . PRIMARY INVESTMENT STRATEGIES         . REDEEMING SHARES
 . THE FUND AND VANGUARD                 . TRANSFERRING REGISTRATION
 . INVESTMENT ADVISER                    . FUND AND ACCOUNT UPDATES
 . DIVIDENDS, CAPITAL GAINS, AND TAXES   GLOSSARY (inside back cover)
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WHY READING THIS PROSPECTUS IS IMPORTANT
This  prospectus  explains the  objective,  risks,  and  strategies  of Vanguard
Calvert Social Index Fund. To highlight  terms and concepts  important to mutual
fund investors,  we have provided "Plain  Talk(R)"  explanations  along the way.
Reading  the  prospectus  will help you to decide  whether the Fund is the right
investment for you. We suggest that you keep it for future reference.
- --------------------------------------------------------------------------------

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IMPORTANT NOTE
Vanguard  Calvert  Social  Index  Fund  offers two  separate  classes of shares:
Investor and Institutional. Investor Shares, which have an investment minimum of
$3,000  ($1,000)  for IRAs),  are  offered by two  separate  prospectuses.  This
prospectus is intended for individual investors and institutional clients. There
is also a prospectus for participants in  employer-sponsored  retirement  plans,
which you can obtain by calling Vanguard at 1-800-523-1188.

Institutional  Shares have an investment minimum of $10 million and generally do
not require special  employee  benefit plan services.  Institutional  Shares are
offered  by  another  prospectus,  which you can  obtain by  calling  Vanguard's
Institutional Investor Group at 1-800-523-1036.

Note that the Fund's separate share classes have different expenses; as a result
their investment performance will vary.
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NEITHER  THE  SECURITIES  AND  EXCHANGE  COMMISSION  NOR  ANY  STATE  SECURITIES
COMMISSION HAS APPROVED OR  DISAPPROVED  OF THESE  SECURITIES OR PASSED UPON THE
ACCURACY OR ADEQUACY OF THIS PROSPECTUS. ANY REPRESENTATION TO THE CONTRARY IS A
CRIMINAL OFFENSE.

<PAGE>


                                                                               1

FUND PROFILE

The following  profile  summarizes key features of Vanguard Calvert Social Index
Fund.

INVESTMENT OBJECTIVE
The Fund seeks to track the  performance of a benchmark  index that measures the
investment return of large- and mid-capitalization stocks.

INVESTMENT STRATEGIES
The Fund employs a passive management strategy designed to track the performance
of the Calvert Social Index.  The Index is composed of large- and mid-cap stocks
that have been  screened for certain  social and  environmental  criteria by the
Index sponsor,  which is independent of Vanguard. The Fund invests in the stocks
that comprise the Index.

PRIMARY RISKS
THE FUND'S TOTAL RETURN,  LIKE STOCK PRICES  GENERALLY,  WILL FLUCTUATE WITHIN A
WIDE  RANGE,  SO AN INVESOR  COULD  LOSE MONEY OVER SHORT OR EVEN LONG  PERIODS.
Stock markets tend to move in cycles,  with periods of rising prices and periods
of falling prices. The Fund is also subject to:
- -    Investment  style risk,  which is the chance that  returns  from large- and
     mid-cap  stocks  generally,  or from stocks  included in the Calvert Social
     Index  specifically,  will trail  returns  from other asset  classes or the
     overall stock market.


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                                PLAIN TALK ABOUT
                                  FUND EXPENSES
All mutual funds have operating  expenses.  These  expenses,  which are deducted
from a fund's gross  income,  are expressed as a percentage of the net assets of
the fund. We expect  Vanguard  Calvert Social Index Fund's expense ratio for the
current  fiscal  year to be .%, or $. per  $1,000 of  average  net  assets.  The
average  multi-cap  mutual fund had  expenses in 1999 of .%, or $. per $1,000 of
average net assets, (derived from data provided by Lipper Inc., which reports on
the mutual fund industry).  Management expenses, which are one part of operating
expenses,  include investment advisory fees as well as other costs of managing a
fund--such  as account  maintenance,  reporting,  accounting,  legal,  and other
administrative expenses.
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FEES AND EXPENSES
The following  table  describes the fees and expenses you may pay if you buy and
hold shares of the Fund. The expenses shown under Annual Fund Operating Expenses
are based upon  estimated  amounts for the current  fiscal year. The Fund has no
operating history, and actual operating expenses could be different.
<PAGE>


2



      SHAREHOLDER FEES (fees paid directly from your investment)
      Sales Charge (Load) Imposed on Purchases:                          None
      Sales Charge (Load) Imposed on Reinvested Dividends:               None
      Redemption Fee:                                                    None
      Exchange Fee:                                                      None
      Account Maintenance Fee (for accounts under $10,000)          $10/year*


      ANNUAL FUND OPERATING EXPENSES (expenses deducted from the
      Fund's assets)
      Management Expenses:                                                 .%
      12b-1 Distribution Fee:                                            None
      Other Expenses:                                                      .%
       TOTAL ANNUAL FUND OPERATING EXPENSES:                            0.25%
      * Vanguard will deduct an account maintenance fee from your
       annual distribution of the Fund's dividends. If your
       distribution is less than the fee, fractional shares will
       be automatically redeemed to make up the difference.

     The following example is intended to help you compare the cost of investing
in the Fund with the cost of investing in other mutual funds. It illustrates the
hypothetical  expenses that you would incur over one-year and three-year periods
if you invest $10,000 in the Fund. This example assumes that the Fund provides a
return of 5% a year,  and that  operating  expenses  match our estimates for the
Fund's first year of operations.The results apply whether or not you redeem your
investment at the end of each period.


                            ------------------------
                              1 YEAR      3 YEARS
                            ------------------------
                                $.           $.
                            ------------------------


THIS  EXAMPLE  SHOULD  NOT  BE  CONSIDERED  TO  REPRESENT   ACTUAL  EXPENSES  OR
PERFORMANCE  FROM THE PAST OR FOR THE  FUTURE.  ACTUAL  FUTURE  EXPENSES  MAY BE
HIGHER OR LOWER THAN THOSE SHOWN.



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ADDITIONAL INFORMATION
DIVIDENDS AND CAPITAL GAINS                       NEWSPAPER ABBREVIATION
Distributed annually in December                  .

INVESTMENT ADVISERS                               VANGUARD FUND NUMBER
The Vanguard Group, Valley Forge, Pa.,            .
since inception
                                                  CUSIP NUMBER
INCEPTION DATE                                    .
May 8, 2000
                                                  TICKER SYMBOL
SUITABLE FOR IRAS                                 .
Yes

MINIMUM INITIAL INVESTMENT
$3,000; $1,000 for IRAs and custodial accounts
for minors
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                                                                               3

AN INTRODUCTION TO INDEX FUNDS

WHAT IS INDEXING?
An index is an unmanaged group of securities  whose overall  performance is used
as a standard to measure the investment  performance of a particular  market. An
index (or "passively managed") fund tries to track, as closely as possible,  the
performance of an established  target index.  The fund does this by holding all,
or a representative sample, of the securities that comprise the index.
     Stock index  funds may seek to track  indexes  that hold a certain  type of
stock--such as growth or value,  small-cap or large-cap,  or those from just one
industry--or  they may seek to track  indexes that consist of a broader range of
stocks--for example the entire U.S. stock market.
     Index funds do not have active managers,  who buy and sell securities based
on research and analysis in an attempt to  outperform a particular  benchmark or
the market as a whole.  Rather,  index funds  simply  attempt to mirror what the
target index does, for better or worse.

WHY INVEST IN INDEX FUNDS?
Index funds appeal to many investors for a number of reasons:
- -    Variety of  investments.  Vanguard index funds  generally  invest in a wide
     variety of companies and industries.
- -    Relative consistency.  Because they seek to track market benchmarks,  index
     funds by  definition  will not  perform  dramatically  better or worse than
     their target indexes.
- -    Low cost.  Index  funds do not have  many of the  expenses  of an  actively
     managed fund, in addition,  they keep trading  activity--and thus brokerage
     commissions--to a minimum.
- -    Low  realization  of capital gains.  Because an index fund typically  sells
     securities only to respond to redemption requests or to adjust its holdings
     to reflect a change in its target index, the fund's turnover rate--and thus
     its  realization of taxable capital  gains--is  usually much lower than the
     average mutual fund.

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                               PLAIN TALK ABOUT
                            THE COSTS OF INVESTING
Costs are an important  consideration in choosing a mutual fund.  That's because
you, as a shareholder,  pay the costs of operating a fund,  plus any transaction
costs  associated with the fund's buying and selling of securities.  These costs
can erode a substantial  portion of the gross income or capital  appreciation  a
fund achieves. Even seemingly small differences in expenses can, over time, have
a dramatic effect on a fund's performance.
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KEEP IN MIND THAT AN INDEX FUND HAS OPERATING  EXPENSES AND TRANSACTION COSTS; A
MARKET INDEX DOES NOT.  THEREFORE,  AN INDEX  FUND--WHILE  EXPECTED TO TRACK ITS
TARGET  INDEX AS  CLOSELY  AS  POSSIBLE--WILL  TYPICALLY  BE UNABLE TO MATCH THE
PERFORMANCE OF THE INDEX EXACTLY.

<PAGE>


4



================================================================================
A WORD ABOUT RISK

This  prospectus  describes  risks you would  face as an  investor  in  Vanguard
Calvert  Social  Index  Fund.  It is  important  to keep in mind one of the main
axioms of  investing:  The  higher  the risk of losing  money,  the  higher  the
potential reward. The reverse,  also, is generally true: The lower the risk, the
lower the  potential  reward.  As you consider an  investment  in the Fund,  you
should also take into account your personal tolerance for the daily fluctuations
of the stock market.
     Look for this [FLAG] symbol  throughout the prospectus.  It is used to mark
detailed  information  about  each  type of risk that you  would  confront  as a
shareholder of the Fund.
================================================================================

WHO SHOULD INVEST

The Fund may be a suitable investment for you if:
- -    You wish to add a fund that invests in large- and mid-capitalization stocks
     to your existing  holdings,  which could include other stock investments as
     well as bond, money market, and tax-exempt investments.
- -    You seek growth of capital over the long-term--at least five years.
- -    You want a fund that considers social and  environmental  issues as part of
     its investment program.

Some  investors  try to profit from a strategy  called  market-timing--switching
money into  investments  when they expect  prices to rise,  and taking money out
when they expect  prices to fall.  As money is shifted in and out, a fund incurs
expenses  for buying and selling  securities.  These costs are borne by all fund
shareholders,  including the long-term  investors who do not generate the costs.
This is why all  Vanguard  funds have  adopted  special  policies to  discourage
short-term trading. Specifically:
- -    Each   Vanguard   fund   reserves   the  right  to  reject   any   purchase
     request--including  exchanges from other Vangaurd funds--that it regards as
     disruptive  to  efficient  portfolio  management.  The  fund  may  reject a
     purchase  request  because of the timing of the  investment or because of a
     history of excessive trading by the investor.
- -    Each  Vanguard  fund (except the money market  funds)  limits the number of
     times that an investor can exchange into and out of the fund.
- -    Each Vanguard fund reserves the right to stop offering shares at any time.
- -    Vanguard's U.S. Stock Index Funds,  International  Stock Index Funds,  REIT
     Index Fund,  Balanced  Index Fund,  and Growth and Income Fund generally do
     NOT accept  exchanges  by  telephone  or fax,  or  online.  (IRAs and other
     retirement accounts are not subject to this rule.)
- -    Certain  Vanguard  funds  charge   transaction  fees  on  purchases  and/or
     redemptions of their shares.
See the INVESTING WITH VANGUARD  section of this  prospectus for further details
on Vanguard's transaction policies.

     THE VANGUARD FUNDS DO NOT PERMIT MARKET-TIMING. DO NOT INVEST WITH VANGUARD
IF YOU ARE A MARKET TIMER.
<PAGE>


                                                                               5

PRIMARY INVESTMENT STRATEGIES
This section explains the strategies that the investment adviser uses in pursuit
of the Fund's investment objective.  It also explains how the adviser implements
these strategies.  In addition,  this section discusses important risks faced by
investors  in the Fund.  The Board of Trustees  oversees the  management  of the
Fund, and may change the investment strategies in the interest of shareholders.


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                               PLAIN TALK ABOUT
                             CALVERT SOCIAL INDEX
The Calvert Social Index is maintained by Calvert Group of Bethesda, Maryland, a
leading  organization in the world of social  investing.  Calvert screens stocks
from  approximately  1,000 of the  largest  companies  in the  United  States by
analyzing each company's record and policies on: environmental issues; workplace
issues;  product safety and impact;  international  operations and human rights;
and weapons contracting.

Calvert  excludes  from the index any  companies  that,  in  Calvert's  opinion,
violate fair labor or equal  opportunity  standards  as well as those  companies
involved with tobacco, alcohol,  gambling, or nuclear power. Companies that pass
Calvert's   screenings  process  are  represented  in  the  index  on  a  market
capitalization-weighted basis.

For further  information about the Calvert Social Index,  please visit Calvert's
web site, at www.calvert.com or contact Calvert at 1-800-368-2745.
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                               PLAIN TALK ABOUT
                         GROWTH FUNDS AND VALUE FUNDS
Growth  investing  and value  investing  are two styles  employed  by stock fund
managers.   Growth  funds  generally   focus  on  companies   believed  to  have
above-average  potential  for growth in revenue  and  earnings.  Reflecting  the
market's high  expectations for superior growth,  such stocks typically have low
dividend  yields  and  above-average  prices in  relation  to such  measures  as
revenue,  earnings,  and book value.  Value funds generally  emphasize stocks of
companies  from which the market does not expect  strong  growth.  The prices of
value  stocks  typically  are  below-average  in  comparison  to such factors as
earnings and book value, and these stocks typically pay  above-average  dividend
yields.  Growth and value stocks have, in the past,  produced similar  long-term
returns,  though each  category has periods when it  outperforms  the other.
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<PAGE>


6

MARKET EXPOSURE

[FLAG] THE FUND IS SUBJECT TO STOCK MARKET RISK,  WHICH IS THE CHANCE THAT STOCK
     PRICES OVERALL WILL DECLINE OVER SHORT OR EVEN LONG PERIODS.  STOCK MARKETS
     TEND TO MOVE IN  CYCLES,  WITH  PERIODS  OF RISING  PRICES  AND  PERIODS OF
     FALLING PRICES.

     To illustrate the volatility of stock prices, the following table shows the
best,  worst,  and average total returns for the U.S.  stock market over various
periods as measured by the Standard & Poor's 500 Index,  a widely used barometer
of market  activity.  (Total returns  consist of dividend  income plus change in
market  price.)  Note that the returns  shown do not include the costs of buying
and selling  stocks or other  expenses  that a real-world  investment  portfolio
would  incur.  Note,  also,  that the gap between best and worst tends to narrow
over the long term.


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                      U.S. STOCK MARKET RETURNS (1926-1999)
- --------------------------------------------------------------------------------
                 1 YEAR       5 YEARS        10 YEARS       20 YEARS
- --------------------------------------------------------------------------------
Best             54.2%        28.6%            19.9%          17.9%
Worst           -43.1        -12.4             -0.9            3.1
Average          13.2         11.0             11.1           11.1
- --------------------------------------------------------------------------------

     The table  covers all of the 1-, 5-,  10-,  and 20-year  periods  from 1926
through 1999. You can see, for example,  that while the average return on stocks
for all of the 5-year periods was 11.0%,  returns for individual  5-year periods
ranged  from a -12.4%  average  (from  1928  through  1932) to 28.6%  (from 1995
through 1999).  These average returns reflect past performance on common stocks;
you should not regard them as an  indication  of future  returns from either the
stock market as a whole or this Fund in particular.



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                               PLAIN TALK ABOUT
                   LARGE-CAP, MID-CAP, AND SMALL-CAP STOCKS
Stocks  of  publicly  traded   companies--and   mutual  funds  that  hold  these
stocks--can be classified by the  companies'  market value,  or  capitalization.
Market  capitalization  changes over time, and there is no "official" definition
of the boundaries of large-,  mid-,  and small-cap  stocks.  Vanguard  generally
defines  large-capitalization  (large-cap)  funds as  those  holding  stocks  of
companies  whose  outstanding  shares have a market value exceeding $12 billion;
mid-cap funds as those holding  stocks of companies  with a market value between
$1 billion and $12  billion;  and  small-cap  funds as those  typically  holding
stocks  of  companies  with a market  value of less  than $1  billion.  Vanguard
periodically reassesses these classifications.
- --------------------------------------------------------------------------------


[FLAG] THE FUND IS ALSO SUBJECT TO  INVESTMENT  STYLE RISK,  WHICH IS THE CHANCE
     THAT RETURNS FROM LARGE- AND  MID-CAPITALIZATION  STOCKS WILL TRAIL RETURNS
     FROM OTHER ASSET CLASSES OR THE OVERALL  STOCK  MARKET.  EACH TYPE OF STOCK
     TENDS TO GO THROUGH CYCLES OF DOING BETTER--OR WORSE--THAN COMMON STOCKS IN
     GENERAL.  THESE PERIODS  HAVE,  IN THE PAST,  LASTED FOR AS LONG AS SEVERAL
     YEARS.
<PAGE>


                                                                               7

RISK OF NONDIVERSIFICATION
[FLAG] As an index  fund,  the Fund will hold the  largest  stocks in its target
index in  approximately  the same percentages as those stocks are represented in
the index. If the target index should become less diversified in the future, the
Fund  similarly  would become less  diversified.  In the unlikely event that the
target index becomes  dominated by just a few companies,  shareholders  would be
subject to the risk that the Fund's performance could be hurt disproportionately
by a decline in the price of just a few stocks.


SECURITY SELECTION
INDEXING METHODS
In seeking to track a particular index, a fund generally uses one of two methods
to select the securities in which it invests.
     REPLICATION   METHOD.   Many  stock  funds--but  not  bond  funds--use  the
replication method of indexing. This means that a fund holds each security found
in its target index in about the same  proportions  as  represented in the index
itself.  For example,  if 5% of the S&P 500 Index were made up of the stock of a
specific company, a fund tracking that index would invest about 5% of its assets
in that company. For bond funds, replication is an inefficient and costly method
of  indexing,  since  there is no liquid  market for many of the  corporate  and
agency bonds typically found in a broad bond index.
     STRAIGHT   SAMPLING  METHOD.   Because  it  would  be  very  expensive  and
inefficient to buy and sell all securities held in certain indexes (the Wilshire
5000 Index, for example,  includes more than 7,000 stocks), funds tracking these
larger   indexes   sometimes  use  a  "straight   sampling"   technique.   Using
sophisticated  computer  programs,  a fund  selects,  from the target  index,  a
representative  sample of securities that will resemble the full target index in
terms of key risk  factors.  For stock  funds,  these key risk  factors  include
industry  weightings,  country  weightings,  market  capitalization,  and  other
financial characteristices of stocks.
     Vanguard Calvert Social Index Fund uses the replication  method of indexing
to invest in stocks.

TURNOVER RATE
Generally,  a  passively  managed  fund  sells  securities  only to  respond  to
redemption  requests  or to adjust the number of shares held to reflect a change
in the fund's target index.
<PAGE>


8


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                               PLAIN TALK ABOUT
                                 TURNOVER RATE
Before  investing in a mutual fund,  you should review its turnover  rate.  This
gives an  indication  of how  transaction  costs could affect the fund's  future
returns.  In general,  the greater the volume of buying and selling by the fund,
the greater the impact that brokerage  commissions and other  transaction  costs
will have on its return. Also, funds with high turnover rates may be more likely
to generate  capital gains that must be  distributed to  shareholders  as income
subject to taxes. The average  turnover rate for all passively  managed domestic
equity index funds  investing  in common  stocks is roughly .%; for all domestic
stock  funds,  the  average  turnover  rate is  approximately  .,  according  to
Morningstar, Inc.
- --------------------------------------------------------------------------------

ACCOUNT MAINTENANCE FEE
Vanguard assesses an account  maintenance fee on index fund  shareholders  whose
account  balances are below $10,000 (for any reason,  including a decline in the
value of a Fund's  shares) on the date a dividend  is  distributed.  This fee is
intended to allocate the costs of  maintaining  accounts  more  equitably  among
shareholders.  The account  maintenance  fee is $10 per year,  deducted from the
annual dividend,  which usually is distributed  during the last two weeks of the
calendar year. If the fee is deducted from your dividend distribution,  you will
still be taxed on the full amount of your dividend  (unless you hold your shares
through a non-taxable  account). If you are due a dividend that is less than the
fee, fractional shares will be automatically redeemed to make up the difference.

OTHER INVESTMENT POLICIES AND RISKS
The Fund  reserves  the right to  substitute  a different  index for the Calvert
Social Index if the Calvert Social Index is discontinued or for any other reason
determined in good faith by the Fund's Board of Trustees. In such instance,  the
substitute index will measure the same general market as the current index.
     The Fund may invest in foreign  securities to the extent necessary to carry
out its investment strategy of holding all of the stocks that comprise the index
it tracks.
     To match its target  index as closely as  possible,  the Fund  attempts  to
remain  fully  invested in stocks.  To help stay fully  invested,  and to reduce
transaction  costs,  the Fund may invest,  to a limited  extent,  in stock index
futures  and  options  contracts,  warrants,  convertible  securities,  and swap
agreements,  which  are  types of  derivatives.  These  investments  will not be
screened based on social or environmental criteria.
     Losses (or gains) involving futures can sometimes be  substantial--in  part
because a relatively small price movement in a futures contract may result in an
immediate and substantial  loss (or gain) for the Fund.  Similar risks exist for
warrants  (securities  that permit their owners to purchase a specific number of
stock shares at a predetermined price),  convertible securities (securities that
may be exchanged for another  asset),  and swap  agreements  (contracts in which
each  party  agrees  to make  payments  to the  other  based on the  return of a
specified index or asset).
     For  this  reason,  the  Fund  will  not use  futures,  options,  warrants,
convertible  securities,  or swap  agreements  for  speculative  purposes  or as
leveraged investments that magnify the gains or losses of an investment.
     The Fund's  obligation to purchase  securities under futures contracts will
not exceed 20% of its total assets.
     The reasons for which the Fund will invest in futures and options are:
<PAGE>


                                                                               9

- -    To keep cash on hand to meet  shareholder  redemptions or other needs while
     simulating full investment in stocks.
- -    To reduce the Fund's  transaction costs or add value when these instruments
     are favorably priced.
     Although index funds, by their nature, tend to be tax-efficient  investment
vehicles, the Fund generally is managed without regard to tax ramifications.

- --------------------------------------------------------------------------------
                                PLAIN TALK ABOUT
                                  DERIVATIVES
A derivative is a financial contract whose value is based on (or "derived" from)
a  traditional  security  (such  as a stock  or a  bond),  an  asset  (such as a
commodity like gold), or a market index (such as the S&P 500 Index). Futures and
options are derivatives  that have been trading on regulated  exchanges for more
than two decades.  These  "traditional"  derivatives are standardized  contracts
that can easily be bought and sold,  and whose market values are  determined and
published  daily. It is these  characteristics  that  differentiate  futures and
options from the relatively new types of derivatives. If used for speculation or
as leveraged investments, derivatives can carry considerable risks.
- --------------------------------------------------------------------------------

THE FUND AND VANGUARD
The Fund is a member of The Vanguard  Group, a family of more than 35 investment
companies  with more than 100 funds  holding  assets worth more than $. billion.
All of the  Vanguard  funds  share  in the  expenses  associated  with  business
operations, such as personnel, office space, equipment, and advertising.
     Vanguard  also  provides   marketing   services  to  the  funds.   Although
shareholders do not pay sales commissions or 12b-1  distribution fees, each fund
pays its allocated share of The Vanguard Group's marketing costs.

- --------------------------------------------------------------------------------
                             PLAIN TALK ABOUT
                     VANGUARD'S UNIQUE CORPORATE STRUCTURE
The Vanguard Group is truly a MUTUAL mutual fund company. It is owned jointly by
the funds it oversees and thus  indirectly by the  shareholders  in those funds.
Most other mutual funds are operated by for-profit management companies that may
be owned by one person,  by a group of individuals,  or by investors who own the
management  company's stock. By contrast,  Vanguard  provides its services on an
"at-cost"  basis,  and the funds' expense  ratios  reflect only these costs.  No
separate  management  company reaps profits or absorbs losses from operating the
funds.
- --------------------------------------------------------------------------------


INVESTMENT ADVISER
The Vanguard Group (Vanguard), P.O. Box 2600, Valley Forge, PA 19482, founded in
1974,  serves as the Fund's adviser  through its Core  Management  Group.  As of
October 31, 1999,  Vanguard  served as adviser for about $346 billion in assets.
Vanguard  manages  the fund on an at-cost  basis,  subject to the control of the
Trustees and officers of the Fund.
<PAGE>


10

     The Fund has  authorized the adviser to choose brokers or dealers to handle
the purchase and sale of securities  for the Fund, and to get the best available
price and most  favorable  execution  from  these  brokers  with  respect to all
transactions.
     Also,  the Fund may  direct  the  adviser  to use a  particular  broker for
certain  transactions  in exchange for commission  rebates or research  services
provided to the Fund.



- --------------------------------------------------------------------------------
                               PLAIN TALK ABOUT
                              THE FUND'S ADVISER
The individual primarily responsible for overseeing the Fund's investments is:

GEORGE U. SAUTER,  Managing  Director of Vanguard,  and head of Vanguard's  Core
Management  Group;  has worked in  investment  management  since  1985;  primary
responsibility  for Vanguard's  stock indexing policy and strategy since joining
the company in 1987; has served as the Fund's portfolio manager since inception;
A.B., Dartmouth College; M.B.A., University of Chicago.
- --------------------------------------------------------------------------------

- --------------------------------------------------------------------------------
                                PLAIN TALK ABOUT
                                 DISTRIBUTIONS
As a  shareholder,  you are  entitled  to your share of the fund's  income  from
interest and dividends, and gains from the sale of investments. You receive such
earnings as either an income  dividend or a capital gains  distribution.  Income
dividends come from both the dividends that the fund earns from its holdings and
the  interest it receives  from its money market and bond  investments.  Capital
gains are realized  whenever the fund sells securities for higher prices than it
paid for them. These capital gains are either short-term or long-term, depending
on whether the fund held the  securities  for one year or less, or more than one
year.
- --------------------------------------------------------------------------------


DIVIDENDS, CAPITAL GAINS, AND TAXES

FUND DISTRIBUTIONS
The Fund  distributes to shareholders  virtually all of its net income (interest
and dividends,  less  expenses),  as well as any capital gains realized from the
sale of its holdings.  Distributions  generally occur in December.  In addition,
the Fund may occasionally be required to make  supplemental  dividend or capital
gains  distributions  at some  other  time  during  the  year.  You can  receive
distributions of income dividends or capital gains in cash, or you can have them
automatically reinvested in more shares of the Fund.

BASIC TAX POINTS

Vanguard will send you a statement  each year showing the tax status of all your
distributions.  In addition,  taxable investors should be aware of the following
basic tax points:
- -    Distributions  are taxable to you whether or not you reinvest these amounts
     in additional Fund shares.
- -    Distributions   declared  in  December--if  paid  to  you  by  the  end  of
     January--are taxable as if received in December.
- -    Any dividends and short-term  capital gains that you receive are taxable to
     you as ordinary income for federal income tax purposes.
<PAGE>


11

- -    Any  distributions  of net  long-term  capital  gains are taxable to you as
     long-term capital gains for federal income tax purposes, no matter how long
     you've owned shares in the Fund.
- -    Capital gains  distributions  may vary  considerably from year to year as a
     result of the Fund's normal investment activities and cash flows.
- -    A sale or exchange of Fund shares is a taxable  event.  This means that you
     may have a capital gain to report as income, or a capital loss to report as
     a deduction, when you complete your federal income tax return.
- -    State and local  income  taxes may apply to any  dividend or capital  gains
     distributions that you receive, as well as to your gains or losses from any
     sale or exchange of Fund shares.

GENERAL INFORMATION

BACKUP  WITHHOLDING.   By  law,  Vanguard  must  withhold  31%  of  any  taxable
distributions  or  redemptions  from your  account if you do not provide us with
your  correct  taxpayer  identification  number and certify  that it is correct.
Similarly,  Vanguard  must withhold from your account if the IRS instructs us to
do so.
FOREIGN  INVESTORS.  The Vanguard funds  generally do not offer their shares for
sale outside of the United States.  Foreign  investors should be aware that U.S.
withholding and estate taxes may apply to any investments in Vanguard funds.
INVALID  ADDRESSES.  If a dividend or capital gains distribution check mailed to
your address of record is returned as undeliverable, Vanguard will automatically
reinvest  all future  distributions  until you  provide us with a valid  mailing
address.
TAX CONSEQUENCES.  This prospectus provides general tax information only. If you
are investing through a tax-deferred retirement account, such as an IRA, special
tax rules apply. Please consult your tax adviser for detailed  information about
a fund's tax consequences for you.


- --------------------------------------------------------------------------------
                                PLAIN TALK ABOUT
                               "BUYING A DIVIDEND"
Unless you are investing through a tax-deferred  retirement  account (such as an
IRA),  it is not to your  advantage  to buy shares of a fund  shortly  before it
makes a  distribution,  because  doing so can cost you money in  taxes.  This is
known as "buying a dividend."  For example:  on December 15, you invest  $5,000,
buying 250 shares for $20 each. If the fund pays a distribution  of $1 per share
on December 16, its share price would drop to $19 (not counting  market change).
You still have only $5,000 (250 shares x $19 = $4,750 in share  value,  plus 250
shares x $1 = $250 in  distributions),  but you owe tax on the $250 distribution
you  received--even  if you  reinvest  it in more  shares.  To avoid  "buying  a
dividend," check a fund's distribution schedule before you invest.
- --------------------------------------------------------------------------------




SHARE PRICE
The Fund's share price,  called its net asset value,  or NAV, is calculated each
business day after the close of regular  trading on the New York Stock  Exchange
(the NAV is not  calculated  on  holidays  or other  days when the  Exchange  is
closed).  Net asset  value per share is computed by adding up the total value of
the Fund's  investments  and other assets,  subtracting  any of its  liabilities
(debts),  and then  dividing  the net assets  attributable  to each class by the
number of Fund shares outstanding for each class.
<PAGE>


12



           NET ASSET VALUE = TOTAL ASSETS - LIABILITIES
                         -------------------------------
                          NUMBER OF SHARES OUTSTANDING




Knowing the daily net asset value is useful to you as a  shareholder  because it
indicates the current value of your  investment.  The Fund's NAV,  multiplied by
the  number of  shares  you own,  gives you the  dollar  amount  you would  have
received had you sold all of your shares back to the Fund that day.
     A NOTE ON PRICING:  The Fund's  investments  will be priced at their market
value when market  quotations are readily  available.  When these quotations are
not  readily  available,  investments  will  be  priced  at  their  fair  value,
calculated according to procedures adopted by the Fund's Board of Trustees.
     The Fund's  share price can be found  daily in the mutual fund  listings of
most major  newspapers  under the  heading  "Vanguard  Index  Funds."  Different
newspapers use different  abbreviations  of the Fund's name, but the most common
is ..






























"Standard & Poor's(R),"  "S&P(R),"  "S&P  500(R),"  "Standard & Poor's 500," and
"500" are trademarks of The McGraw-Hill Companies, Inc.
<PAGE>


                                                                              13



- --------------------------------------------------------------------------------
INVESTING WITH VANGUARD

Are you looking for the most  convenient  way to open or add money to a Vanguard
account?  Obtain instant access to fund information?  Establish an account for a
minor child or for your retirement savings?
     Vanguard  can help.  Our goal is to make it easy and pleasant for you to do
business with us.
     The following  sections of the prospectus briefly explain the many services
we offer.  Booklets providing detailed information are available on the services
marked with a [BOOKLET]. Please call us to request copies.
- --------------------------------------------------------------------------------


SERVICES AND ACCOUNT FEATURES

Vanguard  offers many  services that make it convenient to buy, sell or exchange
shares, or to obtain fund or account information.
- --------------------------------------------------------------------------------
TELEPHONE REDEMPTIONS (SALES AND EXCHANGES)
Automatically set up for this Fund unless you notify us otherwise.
- --------------------------------------------------------------------------------
VANGUARD(R) DIRECT DEPOSIT SERVICE [BOOKLET]
Automatic  method  for  depositing  your  paycheck  or U.S.  government  payment
(including Social Security and government pension checks) into your account.
- --------------------------------------------------------------------------------
VANGUARD(R) AUTOMATIC EXCHANGE SERVICE [BOOKLET]
Automatic  method for  moving a fixed  amount of money  from one  Vanguard  fund
account to another.
- --------------------------------------------------------------------------------
VANGUARD FUND EXPRESS(R) [BOOKLET]
Electronic  method for buying or selling shares.  You can transfer money between
your  Vanguard  fund account and an account at your bank,  savings and loan,  or
credit union on a systematic schedule or whenever you wish.
- --------------------------------------------------------------------------------
VANGUARD DIVIDEND EXPRESS(TM) [BOOKLET]
Electronic method for transferring  dividend and/or capital gains  distributions
directly  from your  Vanguard  fund account to your bank,  savings and loan,  or
credit union account.
- --------------------------------------------------------------------------------
VANGUARD TELE-ACCOUNT(R) 1-800-662-6273 (ON-BOARD)[BOOKLET]
Toll-free  24-hour access to Vanguard fund and account  information--as  well as
some  transactions--by  using any touch-tone phone.  Tele-Account provides total
return,  share price, price change, and yield quotations for all Vanguard funds;
gives your account balances and history (e.g., last transaction, latest dividend
distribution);  and  allows  you to sell or  exchange  shares  to and from  most
Vanguard funds.
- --------------------------------------------------------------------------------
ACCESS VANGUARD/(TM)/ www.vanguard.com [COMPUTER]
You can use your  personal  computer to perform  certain  transactions  for most
Vanguard  funds by accessing our website.  To establish  this service,  you must
register  through our website.  We will then mail you an account access password
that  allows  you  to  process  the  following   financial  and   administrative
transactions online:
- -    Open a new account.*
- -    Buy, sell, or exchange shares of most funds.
- -    Change your name/address.
<PAGE>


                                                                              14

- -    Add/change fund options (including dividend options, Vanguard Fund Express,
     bank instructions,  checkwriting, and Vanguard Automatic Exchange Service).
     (Some  restrictions may apply.) Please call our Client Services  Department
     for assistance.

*Only current Vanguard shareholders can open a new account online, by exchanging
shares from other existing Vanguard accounts.
- --------------------------------------------------------------------------------
INVESTOR INFORMATION DEPARTMENT: 1-800-662-7447 (SHIP) TEXT TELEPHONE:
1-800-952-3335
Call  Vanguard for  information  on our funds,  fund  services,  and  retirement
accounts, and to request literature.
- --------------------------------------------------------------------------------
CLIENT SERVICES DEPARTMENT: 1-800-662-2739 (CREW) TEXT TELEPHONE: 1-800-749-7273
Call Vanguard for information on your account, account transactions, and account
statements.
- --------------------------------------------------------------------------------
SERVICES FOR CLIENTS OF VANGUARD'S INSTITUTIONAL DIVISION: 1-888-809-8102
Vanguard's  Institutional  Division offers a variety of specialized services for
large  institutional   investors,   including  the  ability  to  effect  account
transactions through private electronic networks and third-party recordkeepers.
- --------------------------------------------------------------------------------



TYPES OF ACCOUNTS

Individuals and institutions can establish a variety of accounts with Vanguard.
- --------------------------------------------------------------------------------
FOR ONE OR MORE PEOPLE
Open an account in the name of one (individual) or more (joint tenants) people.
- --------------------------------------------------------------------------------
FOR HOLDING PERSONAL TRUST ASSETS [COMPUTER]
Invest assets held in an existing personal trust.
- --------------------------------------------------------------------------------
FOR INDIVIDUAL RETIREMENT ACCOUNTS [COMPUTER]
Open a  traditional  IRA account or a Roth IRA  account.  Eligibility  and other
requirements  are  established  by federal law and  Vanguard  custodial  account
agreements. For more information, please call 1-800-662-7447 (SHIP).
- --------------------------------------------------------------------------------
FOR AN ORGANIZATION [COMPUTER]
Open an account as a corporation,  partnership,  endowment, foundation, or other
entity.
- --------------------------------------------------------------------------------
FOR THIRD-PARTY TRUSTEE RETIREMENT INVESTMENTS
Open an account as a retirement trust or plan based on an existing  corporate or
institutional  plan.  These  accounts  are  established  by the  trustee  of the
existing plan.
- --------------------------------------------------------------------------------
VANGUARD PROTOTYPE PLANS
Open a  variety  of  retirement  accounts  using  Vanguard  prototype  plans for
individuals,  sole proprietorships,  and small businesses. For more information,
please call 1-800-662-2003.
- --------------------------------------------------------------------------------

- --------------------------------------------------------------------------------
A NOTE ON INVESTING WITH VANGUARD THROUGH OTHER FIRMS
You may purchase or sell Fund shares through a financial  intermediary such as a
bank,  broker,  or investment  adviser.  If you invest with Vanguard  through an
intermediary,  please read that firm's program  materials  carefully to learn of
any  special  rules  that may apply.  For  example,  special  terms may apply to
additional service features, fees, or other policies.  Consult your intermediary
to determine when your order will be priced.
- --------------------------------------------------------------------------------

<PAGE>


                                                                              15

BUYING SHARES

You buy your shares at the Fund's next-determined net asset value after Vanguard
receives your request.  As long as your request is received  before the close of
trading on the New York Stock Exchange,  generally 4 p.m. Eastern time, you will
buy your shares at that day's net asset value.
- --------------------------------------------------------------------------------
MINIMUM INVESTMENT TO . . .
open a new account
$3,000 (regular account); $1,000 (traditional IRAs and Roth IRAs).

add to an existing account
$100 by mail or exchange; $1,000 by wire.
- --------------------------------------------------------------------------------
A NOTE ON LOW BALANCES
The Fund  reserves the right to close any  nonretirement  account  whose balance
falls below the minimum  initial  investment.  The Fund will deduct a $10 annual
fee in June if your nonretirement  account balance at that time is below $2,500.
The low balance fee is waived for investors who have aggregate  Vanguard account
assets of $50,000 or more.
- --------------------------------------------------------------------------------
BY MAIL TO . . .[ENVELOPE]
open a new account
Complete and sign the account registration form and enclose your check.

add to an existing account
Mail your check with an  Invest-By-Mail  form  detached  from your  confirmation
statement to the address listed on the form. Please do not alter  Invest-By-Mail
forms, since they are fund- and account-specific.

Make your check payable to: The Vanguard Group-.
All  purchases  must be made in U.S.  dollars,  and checks must be drawn on U.S.
banks.



First-class mail to:          Express or Registered mail to:
The Vanguard Group            The Vanguard Group
P.O. Box 1110                 455 Devon Park Drive
Valley Forge, PA 19482-1110   Wayne, PA 19087-1815


For clients of Vanguard's Institutional Division . . .


First-class mail to:          Express or Registered mail to:
The Vanguard Group            The Vanguard Group
P.O. Box 2900                 455 Devon Park Drive
Valley Forge, PA 19482-2900   Wayne, PA 19087-1815



- --------------------------------------------------------------------------------
IMPORTANT  NOTE:  To prevent  check fraud,  Vanguard will not accept checks made
payable to third parties.
- --------------------------------------------------------------------------------
BY TELEPHONE TO . . .[TELEPHONE]
open a new account
Call Vanguard  Tele-Account*  24 hours a day--or Client Services during business
hours--to exchange from another Vanguard fund account with the same registration
(name, address,  taxpayer  identification  number, and account type). (Note that
some restrictions apply to index fund accounts.)
<PAGE>


16


add to an existing account
Call Vanguard  Tele-Account*  24 hours a day--or Client Services during business
hours--to exchange from another Vanguard fund account with the same registration
(name, address,  taxpayer  identification  number, and account type). (Note that
some restrictions  apply to index fund accounts.) Use Vanguard Fund Express (see
"Services and Account Features") to transfer assets from your bank account. Call
Client Services before your first use to verify that this option is available.


Vanguard Tele-Account   Client Services
1-800-662-6273          1-800-662-2739



*You must obtain a Personal  Identification Number (PIN) through Tele-Account at
least seven days before you request your first exchange.
- --------------------------------------------------------------------------------
IMPORTANT  NOTE:  Once  you  have  initiated  a  telephone   transaction  and  a
confirmation  number has been assigned,  the transaction  cannot be revoked.  We
reserve the right to refuse any purchase request.
- --------------------------------------------------------------------------------
BY WIRE TO OPEN A NEW ACCOUNT OR ADD TO AN EXISTING ACCOUNT [WIRE]
Call Client  Services to arrange your wire  transaction.  Wire  transactions  to
retirement  accounts are only  available for asset  transfers and rollovers from
other financial institutions.  Individual IRA contributions will not be accepted
by wire.

Wire to:
FRB ABA 021001088
HSBC Bank USA

For credit to:
Account: 000112046
Vanguard Incoming Wire Account

In favor of:
Vanguard Calvert Social Index Fund-.
[Account number, or temporary number for a new account]
[Registered account owner(s)]
[Registered address]
- --------------------------------------------------------------------------------
You can redeem (that is, sell or exchange) shares purchased by check or Vanguard
Fund  Express  at any time.  However,  while  your  redemption  request  will be
processed  at the  next-determined  net asset value after it is  received,  your
redemption  proceeds  will not be available  until  payment for your purchase is
collected, which may take up to ten calendar days.
- --------------------------------------------------------------------------------
A NOTE ON LARGE PURCHASES
It is important that you call Vanguard  before you invest a large dollar amount.
It is our responsibility to consider the interests of all Fund shareholders, and
so we  reserve  the right to refuse any  purchase  that may  disrupt  the Fund's
operation or performance.
- --------------------------------------------------------------------------------

<PAGE>


                                                                              17

REDEEMING SHARES

This section describes how you can redeem--that is, sell or exchange--the Fund's
shares.

When Selling Shares:
- -    Vanguard sends the redemption proceeds to you or a designated third party.*
- -    You can sell all or part of your Fund shares at any time.

*May require a signature guarantee; see footnote on page 18.

When Exchanging Shares:
- -    The redemption proceeds are used to purchase shares of a different Vanguard
     fund.
- -    You must meet the receiving fund's minimum investment requirements.
- -    Vanguard reserves the right to revise or terminate the exchange  privilege,
     limit the amount of an exchange, or reject an exchange at any time, without
     notice.
- -    In  order  to  exchange  into  an  account  with a  different  registration
     (including a different name, address, or taxpayer  identification  number),
     you must include the guaranteed signatures of all current account owners on
     your written instructions.

In both  cases,  your  transaction  will be based on the Fund's  next-determined
share price,  subject to any special  rules  discussed in this  prospectus.  For
exchanges,  the purchase side of the transaction  will be based on the receiving
fund's next-determined share price, again subject to any special rules discussed
in this prospectus.
- --------------------------------------------------------------------------------
NOTE:  Once a redemption  is initiated  and a  confirmation  number  given,  the
transaction CANNOT be canceled.
- --------------------------------------------------------------------------------

HOW TO REQUEST A REDEMPTION
You can request a  redemption  from your Fund  account in any one of three ways:
online, by telephone, or by mail.
     The Vanguard funds whose shares you cannot  exchange online or by telephone
are VANGUARD U.S.  STOCK INDEX FUNDS,  VANGUARD  BALANCED  INDEX FUND,  VANGUARD
INTERNATIONAL  STOCK INDEX FUNDS,  VANGUARD REIT INDEX FUND, and VANGUARD GROWTH
AND INCOME FUND. These funds do, however,  permit online and telephone exchanges
within  IRAs and some other  retirement  accounts.  If you sell  shares of these
funds online, you will receive a redemption check at your address of record.
- --------------------------------------------------------------------------------
ONLINE REQUESTS [COMPUTER]
ACCESS VANGUARD at www.vanguard.com
You can use your personal  computer to sell or exchange  shares of most Vanguard
funds by accessing our website.  To establish  this  service,  you must register
through our website.  We will then mail you an account access password that will
enable  you to sell  or  exchange  shares  online  (as  well  as  perform  other
transactions).
- --------------------------------------------------------------------------------
TELEPHONE REQUESTS [TELEPHONE]
All Account Types Except Retirement:
Call Vanguard  Tele-Account  24 hours a day--or Client  Services during business
hours--to  sell or exchange  shares.  You can exchange  shares from this Fund to
open an account in another Vanguard fund or to add to an existing  Vanguard fund
account with an identical registration.

<PAGE>


18

Retirement Accounts:
You can exchange--but not sell--shares by calling Tele-Account or Client
Services.

Vanguard Tele-Account   Client Services
1-800-662-6273          1-800-662-2739


- --------------------------------------------------------------------------------
SPECIAL  INFORMATION:  We will automatically  establish the telephone redemption
option for your  account,  unless you instruct us  otherwise  in writing.  While
telephone  redemption is easy and convenient,  this account  feature  involves a
risk of loss from  unauthorized or fraudulent  transactions.  Vanguard will take
reasonable  precautions  to protect your  account from fraud.  You should do the
same by keeping your account information  private and immediately  reviewing any
account  statements  that  we  send  to  you.  Make  sure  to  contact  Vanguard
immediately about any transaction you believe to be unauthorized.
- --------------------------------------------------------------------------------
We reserve the right to refuse a telephone redemption if the caller is unable to
provide:
- -    The ten-digit account number.
- -    The name and address exactly as registered on the account.
- -    The primary Social Security or employer identification number as registered
     on the account.
- -    The Personal  Identification  Number (PIN),  if applicable  (for  instance,
     Tele-Account).

     Please note that Vanguard will not be  responsible  for any account  losses
due to telephone  fraud, so long as we have taken reasonable steps to verify the
caller's identity.  If you wish to remove the telephone  redemption feature from
your account, please notify us in writing.
- --------------------------------------------------------------------------------
A NOTE ON UNUSUAL CIRCUMSTANCES
Vanguard  reserves the right to revise or  terminate  the  telephone  redemption
privilege at any time,  without notice.  In addition,  Vanguard can stop selling
shares or postpone  payment at times when the New York Stock  Exchange is closed
or under any emergency  circumstances  as determined by the U.S.  Securities and
Exchange Commission.  If you experience difficulty making a telephone redemption
during  periods  of  drastic  economic  or market  change,  you can send us your
request  by  regular or express  mail.  Follow  the  instructions  on selling or
exchanging shares by mail in this section.
- --------------------------------------------------------------------------------
MAIL REQUESTS [ENVELOPE]
All Account Types Except Retirement:
Send a letter of instruction signed by all registered  account holders.  Include
the fund name and  account  number and (if you are  selling) a dollar  amount or
number  of shares  OR (if you are  exchanging)  the name of the fund you want to
exchange  into and a dollar  amount or number of  shares.  To  exchange  into an
account  with a different  registration  (including a different  name,  address,
taxpayer identification number, or account type), you must provide Vanguard with
written  instructions  that  include the  guaranteed  signatures  of all current
owners of the fund from which you wish to redeem.

Vanguard Retirement Accounts:
For information on how to request distributions from:
- -    Traditional IRAs and Roth IRAs--call Client Services.
- -    SEP-IRAs, SIMPLE IRAs, 403(b)(7) custodial accounts, and Profit-Sharing and
     Money Purchase Pension (Keogh) Plans--call  Individual  Retirement Plans at
     1-800-662-2003.

Depending on your account  registration  type,  additional  documentation may be
required.
<PAGE>


                                                                              19



First-class mail to:          Express or Registered mail to:
The Vanguard Group            The Vanguard Group
P.O. Box 1110                 455 Devon Park Drive
Valley Forge, PA 19482-1110   Wayne, PA 19087-1815



For clients of Vanguard's Institutional Division .  .  .


First-class mail to:          Express or Registered mail to:
The Vanguard Group            The Vanguard Group
P.O. Box 2900                 455 Devon Park Drive
Valley Forge, PA 19482-2900   Wayne, PA 19087-1815


- --------------------------------------------------------------------------------
A NOTE ON LARGE REDEMPTIONS
It is important that you call Vanguard  before you redeem a large dollar amount.
It is our responsibility to consider the interests of all fund shareholders, and
so we reserve the right to delay  delivery of your  redemption  proceeds--up  to
seven days--if the amount may disrupt the Fund's operation or performance.
     If you redeem more than  $250,000  worth of fund  shares  within any 90-day
period,  the  Fund  reserves  the  right  to pay  part or all of the  redemption
proceeds above $250,000  in-kind,  i.e., in securities,  rather than in cash. If
payment is made in-kind,  you may incur  brokerage  commissions  if you elect to
sell the securities for cash.
- --------------------------------------------------------------------------------


OPTIONS FOR REDEMPTION PROCEEDS
You may receive your redemption  proceeds in one of three ways: check,  exchange
to another Vanguard fund, or Fund Express redemption.
- --------------------------------------------------------------------------------
CHECK REDEMPTIONS
Normally,  Vanguard  will  mail  your  check  within  two  business  days  of  a
redemption.
- --------------------------------------------------------------------------------
EXCHANGE REDEMPTIONS
As described  above, an exchange  involves using the proceeds of your redemption
to purchase shares of another Vanguard fund.
- --------------------------------------------------------------------------------
FUND EXPRESS REDEMPTIONS
Vanguard  will  electronically  transfer  funds to your  pre-linked  checking or
savings account.
- --------------------------------------------------------------------------------


FOR OUR MUTUAL PROTECTION
For your best interests and ours, Vanguard applies these additional requirements
to redemptions:

REQUEST IN "GOOD ORDER"
All redemption requests must be received by Vanguard in "good order." This means
that your request must include:
- -    The Fund name and account number.
- -    The amount of the transaction (in dollars or shares).
- -    Signatures  of all owners  exactly as  registered  on the account (for mail
     requests).
- -    Signature guarantees (if required).*
- -    Any supporting legal documentation that may be required.
- -    Any outstanding certificates representing shares to be redeemed.

*For instance,  a signature guarantee must be provided by all registered account
shareholders  when redemption  proceeds are to be sent to a different  person or
address. A signature  guarantee may be obtained from most commercial and savings
banks, credit unions, trust companies, or member firms of a U.S. stock exchange.

<PAGE>


20

TRANSACTIONS ARE PROCESSED AT THE NEXT-DETERMINED SHARE PRICE AFTER VANGUARD HAS
RECEIVED ALL REQUIRED INFORMATION.
- --------------------------------------------------------------------------------
LIMITS ON ACCOUNT ACTIVITY
Because  excessive  account  transactions can disrupt the management of the Fund
and increase  the Fund's costs for all  shareholders,  Vanguard  limits  account
activity as follows:
- -    You may make no more than TWO  SUBSTANTIVE  "ROUND TRIPS"  THROUGH THE FUND
     during any 12-month period.
- -    Your round trips through the Fund must be at least 30 days apart.
- -    The Fund may refuse a share purchase at any time, for any reason.
- -    Vanguard may revoke an investor's telephone exchange privilege at any time,
     for any reason.

A "round trip" is a redemption  from the Fund  followed by a purchase  back into
the  Fund.  Also  a  "round  trip"  covers  transactions   accomplished  by  any
combination  of methods,  including  transactions  conducted by check,  wire, or
exchange to/from another Vanguard fund. "Substantive" means a dollar amount that
Vanguard  determines,  in  its  sole  discretion,  could  adversely  affect  the
management of the Fund.
- --------------------------------------------------------------------------------
RETURN YOUR SHARE CERTIFICATES
Any portion of your account represented by share certificates cannot be redeemed
until you return the  certificates  to Vanguard.  Certificates  must be returned
(unsigned),  along with a letter  requesting  the sale or  exchange  you wish to
process, via certified mail to:

The Vanguard Group
455 Devon Park Drive
Wayne, PA 19087-1815
- --------------------------------------------------------------------------------
ALL TRADES ARE FINAL
Vanguard  will not cancel any  transaction  request  (including  any purchase or
redemption)  that we believe to be authentic once the request has been initiated
and a confirmation number assigned.
- --------------------------------------------------------------------------------
UNCASHED CHECKS
Please cash your distribution or redemption  checks promptly.  Vanguard will not
pay interest on uncashed checks.
- --------------------------------------------------------------------------------



TRANSFERRING REGISTRATION

You can  transfer  the  registration  of your Fund  shares to  another  owner by
completing a transfer form and sending it to Vanguard.


First-class mail to:          Express or Registered mail to:
The Vanguard Group            The Vanguard Group
P.O. Box 1110                 455 Devon Park Drive
Valley Forge, PA 19482-1110   Wayne, PA 19087-1815




<PAGE>


                                                                              21

For clients of Vanguard's Institutional Division . . .


First-class mail to:          Express or Registered mail to:

The Vanguard Group            The Vanguard Group
P.O. Box 2900                 455 Devon Park Drive
Valley Forge, PA 19482-2900   Wayne, PA 19087-1815



FUND AND ACCOUNT UPDATES

STATEMENTS AND REPORTS
We will send you account and tax  statements to help you keep track of your Fund
account  throughout  the year as well as when you are preparing  your income tax
returns.
     In addition,  you will  receive  financial  reports  about the Fund twice a
year.  These   comprehensive   reports  include  an  assessment  of  the  Fund's
performance  (and a comparison  to its industry  benchmark),  an overview of the
financial  markets,  a  report  from  the  advisers,  and the  Fund's  financial
statements which include a listing of the Fund's holdings.
     To keep  the  Fund's  costs  as low as  possible  (so  that  you and  other
shareholders can keep more of the Fund's investment earnings), Vanguard attempts
to  eliminate  duplicate  mailings  to the same  address.  When two or more Fund
shareholders  have the same last name and address,  we send just one Fund report
to that address--instead of mailing separate reports to each shareholder. If you
want us to send  separate  reports,  notify our Client  Services  Department  at
1-800-662-2739.
- --------------------------------------------------------------------------------
CONFIRMATION STATEMENT
Sent each time you buy,  sell, or exchange  shares;  confirms the trade date and
the amount of your transaction.
- --------------------------------------------------------------------------------
PORTFOLIO SUMMARY [BOOKLET]
Mailed  quarterly for most  accounts;  shows the market value of your account at
the close of the statement period, as well as distributions,  purchases,  sales,
and exchanges for the current calendar year.
- --------------------------------------------------------------------------------
FUND FINANCIAL REPORTS
Mailed in October and April for this Fund.
- --------------------------------------------------------------------------------
TAX STATEMENTS
Generally  mailed in January;  report previous year's dividend and capital gains
distributions,  proceeds from the sale of shares, and distributions from IRAs or
other retirement accounts.
- --------------------------------------------------------------------------------
AVERAGE COST REVIEW STATEMENT [BOOKLET]
Issued quarterly for most taxable accounts (accompanies your Portfolio Summary);
shows the average  cost of shares that you redeemed  during the  calendar  year,
using only the average cost single category method.
- --------------------------------------------------------------------------------

<PAGE>

GLOSSARY OF INVESTMENT TERMS


ACTIVE MANAGEMENT
An investment approach that seeks to exceed the average returns of the financial
markets.  Active  managers  rely on research,  market  forecasts,  and their own
judgment and experience in selecting securities to buy and sell.

CAPITAL GAINS DISTRIBUTION
Payment to mutual fund shareholders of gains realized on securities that a fund
has sold at a profit, minus any realized losses.

CASH RESERVES
Cash deposits,  short-term  bank deposits,  and money market  instruments  which
include U.S.  Treasury bills,  bank  certificates  of deposit (CDs),  repurchase
agreements, commercial paper, and banker's acceptances.

COMMON STOCK
A security  representing  ownership  rights in a  corporation.  A stockholder is
entitled  to share in the  company's  profits,  some of which may be paid out as
dividends.

DIVIDEND INCOME
Payment to  shareholders  of income from  interest or  dividends  generated by a
fund's investments.

EXPENSE RATIO
The  percentage  of a fund's  average net assets used to pay its  expenses.  The
expense ratio  includes  management  fees,  administrative  fees,  and any 12b-1
distribution fees.

INDEX
An unmanaged group of securities whose overall performance is used as a standard
to measure investment performance.

INVESTMENT ADVISER
An  organization  that  makes  the  day-to-day   decisions  regarding  a  fund's
investments.

MUTUAL FUND
An  investment  company  that pools the money of many people and invests it in a
variety of securities in an effort to achieve a specific objective over time.

NET ASSET VALUE (NAV)
The market value of a mutual fund's total assets, minus liabilities,  divided by
the  number of shares  outstanding.  The value of a single  share is called  its
share value or share price.

PASSIVE MANAGEMENT
A low-cost  investment strategy in which a mutual fund attempts to match--rather
than  outperform--a  particular  stock  or bond  market  index.  Also  known  as
indexing.

PRINCIPAL
The amount of your own money you put into an investment.

SECURITIES
Stocks, bonds, money market instruments, and other investment vehicles.

TOTAL RETURN
A percentage change,  over a specified time period, in a mutual fund's net asset
value,  with the ending net asset value adjusted to account for the reinvestment
of all distributions of dividends and capital gains.

VOLATILITY
The  fluctuations  in value of a mutual  fund or other  security.  The greater a
fund's volatility, the wider the fluctuations between its high and low prices.

YIELD
Income  (interest  or  dividends)  earned  by  an  investment,  expressed  as  a
percentage of the investment's price.
<PAGE>

[SHIP]
[THE VANGUARD GROUP LOGO]
Post Office Box 2600
Valley Forge, PA 19482-2600

FOR MORE INFORMATION
If you'd like more information about
Vanguard Calvert Social Index Fund,
the following documents are
available free upon request:

ANNUAL/SEMIANNUAL REPORTS TO
SHAREHOLDERS
Additional information about the
Fund's investments is available in
the Fund's annual and semiannual
reports to shareholders.

STATEMENT OF ADDITIONAL
INFORMATION (SAI)
The SAI provides more detailed
information about the Fund.

The current annual and semiannual
reports and the SAI are incorporated
by reference into (and are thus
legally a part of) this prospectus.

To receive a free copy of the latest
annual or semiannual report or the
SAI, or to request additional
information about the Fund or other
Vanguard funds, please contact us
as follows:

THE VANGUARD GROUP
INVESTOR INFORMATION
DEPARTMENT
P.O. BOX 2600
VALLEY FORGE, PA
19482-2600

TELEPHONE: 1-800-662-7447 (SHIP)

TEXT TELEPHONE: 1-800-952-3335

WORLD WIDE WEB:
WWW.VANGUARD.COM

If you are a current Fund shareholder
and would like information about
your account, account transactions,
and/or account statements,
please call:

CLIENT SERVICES DEPARTMENT
TELEPHONE:
1-800-662-2739 (CREW)

TEXT TELEPHONE:
1-800-749-7273

INFORMATION PROVIDED BY THE
SECURITIES AND EXCHANGE
COMMISSION (SEC)
You can review and copy
information about the Fund
(including the SAI) at the SEC's
Public Reference Room in
Washington, DC. To find out more
about this public service, call the
SEC at 1-800-SEC-0330. Reports and
other information about the Fund are
also available on the SEC's website
(www.sec.gov), or you can receive
copies of this information, for a fee,
by writing the Public Reference
Section, Securities and Exchange
Commission, Washington, DC 20549-0102.

Fund's Investment Company Act file
number: 811-1027

(C) 2000 The Vanguard Group, Inc.
All rights reserved.
Vanguard Marketing Corporation,
Distributor.

 .-04/28/2000
<PAGE>

VANGUARD(R) CALVERT SOCIAL INDEX FUND

Participant Prospectus
April 28, 2000


This is the Fund's initial
prospectus, so it contains
no performance data.


[A MEMBER OF
THE VANGUARD GROUP LOGO]

<PAGE>

VANGUARD CALVERT SOCIAL INDEX FUND
Prospectus
April 28, 2000

A Stock Index Mutual Fund

- --------------------------------------------------------------------------------
CONTENTS
- --------------------------------------------------------------------------------
 . FUND PROFILE                     . INVESTMENT ADVISER
 . ADDITIONAL INFORMATION           . DIVIDENDS, CAPITAL GAINS, AND TAXES
 . AN INTRODUCTION TO INDEX FUNDS   . SHARE PRICE
 . A WORD ABOUT RISK                . INVESTING WITH VANGUARD
 . WHO SHOULD INVEST                . ACCESSING FUND INFORMATION BY COMPUTER
 . PRIMARY INVESTMENT STRATEGIES    GLOSSARY (inside back cover)
 . THE FUND AND VANGUARD
- --------------------------------------------------------------------------------


- --------------------------------------------------------------------------------
WHY READING THIS PROSPECTUS IS IMPORTANT

This  prospectus  explains the  objective,  risks,  and  strategies  of Vanguard
Calvert Social Index Fund. To highlight  terms and concepts  important to mutual
fund investors,  we have provided "Plain Talk/(R)/"  explanations along the way.
Reading  the  prospectus  will help you to decide  whether the Fund is the right
investment for you. We suggest that you keep it for future reference.
- -------------------------------------------------------------------------------

- --------------------------------------------------------------------------------
IMPORTANT NOTE

Vanguard  Calvert  Social  Index  Fund  offers two  separate  classes of shares:
Investor and Institutional. Investor Shares, which have an investment minimum of
$3,000  ($1,000  for IRAs),  are  offered  by two  separate  prospectuses.  This
prospectus  is intended for  participants  in  employer-sponsored  retirement or
savings plans. Another version--for  investors who would like to open a personal
investment account--can be obtained by calling Vanguard at 1-800-662-7447.

Institutional  Shares have an investment minimum of $10 million and generally do
not require special  employee  benefit plan services.  Institutional  Shares are
offered  by  another  prospectus,  which you can  obtain by  calling  Vanguard's
Institutional Investor Group at 1-800-523-1036.

Note that the Fund's  separate  share  classes  have  different  expenses;  as a
result, their investment performances will vary.
- -------------------------------------------------------------------------------









NEITHER  THE  SECURITIES  AND  EXCHANGE  COMMISSION  NOR  ANY  STATE  SECURITIES
COMMISSION HAS APPROVED OR  DISAPPROVED  OF THESE  SECURITIES OR PASSED UPON THE
ACCURACY OR ADEQUACY OF THIS PROSPECTUS. ANY REPRESENTATION TO THE CONTRARY IS A
CRIMINAL OFFENSE.
<PAGE>


                                                                               1

FUND PROFILE

The following  profile  summarizes key features of Vanguard Calvert Social Index
Fund.

INVESTMENT OBJECTIVE
The Fund seeks to track the  performance of a benchmark  index that measures the
investment return of large- and mid-capitalization stocks.

INVESTMENT STRATEGIES
The Fund employs a passive management strategy designed to track the performance
of the Calvert Social Index.  The index is composed of large- and mid-cap stocks
that have been  screened for certain  social and  environmental  criteria by the
index sponsor,  which is independent of Vanguard. The Fund invests in the stocks
that comprise the Index.

PRIMARY RISKS
THE FUND'S TOTAL RETURN,  LIKE STOCK PRICES  GENERALLY,  WILL FLUCTUATE WITHIN A
WIDE  RANGE,  SO AN INVESTOR  COULD LOSE MONEY OVER SHORT OR EVEN LONG  PERIODS.
Stock markets tend to move in cycles,  with periods of rising prices and periods
of falling prices. The Fund is also subject to:
- -    Investment  style risk,  which is the chance that  returns  from large- and
     mid-cap  stocks  generally,  or from stocks  included in the Calvert Social
     Index  specifically,  will trail  returns  from other asset  classes or the
     overall stock market.

- --------------------------------------------------------------------------------
                               PLAIN TALK ABOUT
                                 FUND EXPENSES
All mutual funds have operating  expenses.  These  expenses,  which are deducted
from a fund's gross  income,  are expressed as a percentage of the net assets of
the fund. We expect  Vanguard  Calvert Social Index Fund's expense ratio for the
current  fiscal  year to be .%, or $. per  $1,000 of  average  net  assets.  The
average  multi-cap  mutual fund had  expenses in 1999 of .%, or $. per $1,000 of
average net assets, (derived from data provided by Lipper Inc., which reports on
the mutual fund industry).  Management expenses, which are one part of operating
expenses,  include investment advisory fees as well as other costs of managing a
fund--such  as account  maintenance,  reporting,  accounting,  legal,  and other
administrative expenses.
- --------------------------------------------------------------------------------



FEES AND EXPENSES
The following table describes the fees and expenses you would pay if you buy and
hold shares of the Fund. The expenses shown under Annual Fund Operating Expenses
are based upon  estimated  amounts for the current  fiscal year. The Fund has no
operating history, and actual operating expenses could be different.
<PAGE>


2



      SHAREHOLDER FEES (fees paid directly from your investment)
      Sales Charge (Load) Imposed on Purchases:               None
      Sales Charge (Load) Imposed on Reinvested Dividends:    None
      Redemption Fee:                                         None
      Exchange Fee:                                           None


      ANNUAL FUND OPERATING EXPENSES (expenses deducted from the
      Fund's assets)
      Management Expenses:                                      .%
      12b-1 Distribution Fee:                                 None
      Other Expenses:                                           .%
       TOTAL ANNUAL FUND OPERATING EXPENSES:                 0.25%



     The following example is intended to help you compare the cost of investing
in the Fund with the cost of investing in other mutual funds. It illustrates the
hypothetical  expenses that you would incur over one-year and three-year periods
if you invest $10,000 in the Fund. This example assumes that the Fund provides a
return of 5% a year,  and that  operating  expenses  match our estimates for the
Fund's first year of operations.The results apply whether or not you redeem your
investment at the end of each period.


                            ------------------------
                               1 YEAR   3 YEARS
                            ------------------------
                                 $.         $.
                            ------------------------

     THIS  EXAMPLE  SHOULD NOT BE  CONSIDERED  TO REPRESENT  ACTUAL  EXPENSES OR
PERFORMANCE  FROM THE PAST OR FOR THE  FUTURE.  ACTUAL  FUTURE  EXPENSES  MAY BE
HIGHER OR LOWER THAN THOSE SHOWN.


- --------------------------------------------------------------------------------
ADDITIONAL INFORMATION
DIVIDENDS AND CAPITAL GAINS              NEWSPAPER ABBREVIATION
Distributed annually in December         .

INVESTMENT ADVISERS                      VANGUARD FUND NUMBER
The Vanguard Group, Valley Forge, Pa.,   .
since inception
                                         CUSIP NUMBER
INCEPTION DATE                           .
May 8, 2000
                                         TICKER SYMBOL
                                         .
- --------------------------------------------------------------------------------

AN INTRODUCTION TO INDEX FUNDS

WHAT IS INDEXING?
An index is an unmanaged group of securities  whose overall  performance is used
as a standard to measure the investment  performance of a particular  market. An
index (or "passively managed") fund tries to track, as closely as possible,  the
performance of an established  target index.  The fund does this by holding all,
or a representative sample, of the securities that comprise the index.
     Stock index  funds may seek to track  indexes  that hold a certain  type of
stock--such as growth or value,  small-cap or large-cap,  or those from just one
industry--or they may seek
<PAGE>


                                                                               3

to track  indexes that  consist of a broader  range of  stocks--for  example the
entire U.S. stock market.
     Index funds do not have active managers,  who buy and sell securities based
on research and analysis in an attempt to  outperform a particular  benchmark or
the market as a whole.  Rather,  index funds  simply  attempt to mirror what the
target index does, for better or worse.

WHY INVEST IN INDEX FUNDS?
Index funds appeal to many investors for a number of reasons:
- -    Variety of  investments.  Vanguard index funds  generally  invest in a wide
     variety of companies and industries.
- -    Relative consistency.  Because they seek to track market benchmarks,  index
     funds by  definition  will not  perform  dramatically  better or worse than
     their target indexes.
- -    Low cost.  Index  funds do not have  many of the  expenses  of an  actively
     managed fund, in addition,  they keep trading  activity--and thus brokerage
     commissions--to a minimum.
- -    Low  realization  of capital gains.  Because an index fund typically  sells
     securities only to respond to redemption requests or to adjust its holdings
     to reflect a change in its target index, the fund's turnover rate--and thus
     its  realization of taxable capital  gains--is  usually much lower than the
     average mutual fund.


- --------------------------------------------------------------------------------
                               PLAIN TALK ABOUT
                            THE COSTS OF INVESTING
Costs are an important  consideration in choosing a mutual fund.  That's because
you, as a shareholder,  pay the costs of operating a fund,  plus any transaction
costs  associated with the fund's buying and selling of securities.  These costs
can erode a substantial  portion of the gross income or capital  appreciation  a
fund achieves. Even seemingly small differences in expenses can, over time, have
a dramatic effect on a fund's performance.
- --------------------------------------------------------------------------------

     KEEP IN MIND THAT AN INDEX  FUND HAS  OPERATING  EXPENSES  AND  TRANSACTION
COSTS;  A MARKET INDEX DOES NOT.  THEREFORE,  AN INDEX  FUND--WHILE  EXPECTED TO
TRACK ITS TARGET INDEX AS CLOSELY AS POSSIBLE--WILL TYPICALLY BE UNABLE TO MATCH
THE PERFORMANCE OF THE INDEX EXACTLY.

- --------------------------------------------------------------------------------

================================================================================
A WORD ABOUT RISK

This  prospectus  describes  risks you would  face as an  investor  in  Vanguard
Calvert  Social  Index  Fund.  It is  important  to keep in mind one of the main
axioms of  investing:  The  higher  the risk of losing  money,  the  higher  the
potential reward. The reverse,  also, is generally true: The lower the risk, the
lower the  potential  reward.  As you consider an  investment  in the Fund,  you
should also take into account your personal tolerance for the daily fluctuations
of the stock market.
     Look for this [FLAG] symbol  throughout the prospectus.  It is used to mark
detailed  information  about  each  type of risk that you  would  confront  as a
shareholder of the Fund.
================================================================================

<PAGE>


4

WHO SHOULD INVEST

The Fund may be a suitable investment for you if:
- -    You wish to add a fund that invests in large- and mid-capitalization stocks
     to your existing  holdings,  which could include other stock investments as
     well as bond, money market, and tax-exempt investments.
- -    You seek growth of capital over the long-term--at least five years.
- -    You want a fund that considers social and  environmental  issues as part of
     its investment program.

Some  investors  try to profit from a strategy  called  market-timing--switching
money into  investments  when they expect  prices to rise,  and taking money out
when they expect  prices to fall.  As money is shifted in and out, a fund incurs
expenses  for buying and selling  securities.  These costs are borne by all fund
shareholders,  including the long-term  investors who do not generate the costs.
This is why all  Vanguard  funds have  adopted  special  policies to  discourage
short-term trading. Specifically:
- -    Each   Vanguard   fund   reserves   the  right  to  reject   any   purchase
     request--including  exchanges from other Vangaurd funds--that it regards as
     disruptive  to  efficient  portfolio  management.  The  fund  may  reject a
     purchase  request  because of the timing of the  investment or because of a
     history of excessive trading by the investor.
- -    Each  Vanguard  fund (except the money market  funds)  limits the number of
     times that an investor can exchange into and out of the fund.
- -    Each Vanguard fund reserves the right to stop offering shares at any time.
- -    Vanguard's U.S. Stock Index Funds,  International  Stock Index Funds,  REIT
     Index Fund,  Balanced  Index Fund,  and Growth and Income Fund generally do
     NOT accept  exchanges  by  telephone  or fax,  or  online.  (IRAs and other
     retirement accounts are not subject to this rule.)
- -    Certain  Vanguard  funds  charge   transaction  fees  on  purchases  and/or
     redemptions of their shares.
See the INVESTING WITH VANGUARD  section of this  prospectus for further details
on Vanguard's transaction policies.

     THE VANGUARD FUNDS DO NOT PERMIT MARKET-TIMING. DO NOT INVEST WITH VANGUARD
IF YOU ARE A MARKET TIMER.


PRIMARY INVESTMENT STRATEGIES

This section explains the strategies that the investment adviser uses in pursuit
of the Fund's investment objective.  It also explains how the adviser implements
these strategies.  In addition,  this section discusses important risks faced by
investors  in the Fund.  The Board of Trustees  oversees the  management  of the
Fund, and may change the investment strategies in the interest of shareholders.
<PAGE>


                                                                               5

- --------------------------------------------------------------------------------
                               PLAIN TALK ABOUT
                             CALVERT SOCIAL INDEX


The Calvert Social Index is maintained by Calvert Group of Bethesda, Maryland, a
leading  organization in the world of social  investing.  Calvert screens stocks
from  approximately  1,000 of the  largest  companies  in the  United  States by
analyzing each company's record and policies on: environmental issues; workplace
issues;  product safety and impact;  international  operations and human rights;
and weapons contracting.

Calvert excludes from the index any companies that,in Calvert's opinion, violate
fair labor or equal  opportunity  standards as well as those companies  involved
with tobacco, alcohol, gambling, or nuclear power. Companies that pass Calvert's
screenings    process   are    represented    in   the   index   on   a   market
capitalization-weighted basis.

For further  information about the Calvert Social Index,  please visit Calvert's
web site, at www.calvert.com or contact Calvert at 1-800-368-2745.
- --------------------------------------------------------------------------------


- --------------------------------------------------------------------------------
                               PLAIN TALK ABOUT
                         GROWTH FUNDS AND VALUE FUNDS
Growth  investing  and value  investing  are two styles  employed  by stock fund
managers.   Growth  funds  generally   focus  on  companies   believed  to  have
above-average  potential  for growth in revenue  and  earnings.  Reflecting  the
market's high  expectations for superior growth,  such stocks typically have low
dividend  yields  and  above-average  prices in  relation  to such  measures  as
revenue,  earnings,  and book value.  Value funds generally  emphasize stocks of
companies  from which the market does not expect  strong  growth.  The prices of
value  stocks  typically  are  below-average  in  comparison  to such factors as
earnings and book value, and these stocks typically pay  above-average  dividend
yields.  Growth and value stocks have, in the past,  produced similar  long-term
returns,  though each  category has periods when it  outperforms  the other.
- --------------------------------------------------------------------------------

MARKET EXPOSURE

[FLAG]THE FUND IS SUBJECT TO STOCK MARKET  RISK,  WHICH IS THE CHANCE THAT STOCK
     PRICES OVERALL WILL DECLINE OVER SHORT OR EVEN LONG PERIODS.  STOCK MARKETS
     TEND TO MOVE IN  CYCLES,  WITH  PERIODS  OF RISING  PRICES  AND  PERIODS OF
     FALLING PRICES.

     To illustrate the volatility of stock prices, the following table shows the
best,  worst,  and average total returns for the U.S.  stock market over various
periods as measured by the Standard & Poor's 500 Index,  a widely used barometer
of market  activity.  (Total returns  consist of dividend  income plus change in
market  price.)  Note that the returns  shown do not include the costs of buying
and selling stocks or other expenses that a real-world invest-
<PAGE>


                                                                               6

ment  portfolio  would incur.  Note,  also,  that the gap between best and worst
tends to narrow over the long term.

- --------------------------------------------------------------------------------
                      U.S. STOCK MARKET RETURNS (1926-1999)
- --------------------------------------------------------------------------------
                 1 YEAR       5 YEARS             10 YEARS       20 YEARS
- --------------------------------------------------------------------------------
Best              54.2%        28.6%                19.9%          17.9%
Worst            -43.1        -12.4                 -0.9            3.1
Average           13.2         11.0                 11.1           11.1
- --------------------------------------------------------------------------------

     The table  covers all of the 1-, 5-,  10-,  and 20-year  periods  from 1926
through 1999. You can see, for example,  that while the average return on stocks
for all of the 5-year periods was 11.0%,  returns for individual  5-year periods
ranged  from a -12.4%  average  (from  1928  through  1932) to 28.6%  (from 1995
through 1999).  These average returns reflect past performance on common stocks;
you should not regard them as an  indication  of future  returns from either the
stock market as a whole or this Fund in particular.



- --------------------------------------------------------------------------------
                               PLAIN TALK ABOUT
                   LARGE-CAP, MID-CAP, AND SMALL-CAP STOCKS
Stocks  of  publicly  traded   companies--and   mutual  funds  that  hold  these
stocks--can be classified by the  companies'  market value,  or  capitalization.
Market  capitalization  changes over time, and there is no "official" definition
of the boundaries of large-,  mid-,  and small-cap  stocks.  Vanguard  generally
defines  large-capitalization  (large-cap)  funds as  those  holding  stocks  of
companies  whose  outstanding  shares have a market value exceeding $12 billion;
mid-cap funds as those holding  stocks of companies  with a market value between
$1 billion and $12  billion;  and  small-cap  funds as those  typically  holding
stocks  of  companies  with a market  value of less  than $1  billion.  Vanguard
periodically reassesses these classifications.
- --------------------------------------------------------------------------------



[FLAG] THE FUND IS ALSO SUBJECT TO  INVESTMENT  STYLE RISK,  WHICH IS THE CHANCE
     THAT RETURNS FROM LARGE- AND  MID-CAPITALIZATION  STOCKS WILL TRAIL RETURNS
     FROM OTHER ASSET CLASSES OR THE OVERALL  STOCK  MARKET.  EACH TYPE OF STOCK
     TENDS TO GO THROUGH CYCLES OF DOING BETTER--OR WORSE--THAN COMMON STOCKS IN
     GENERAL.  THESE PERIODS  HAVE,  IN THE PAST,  LASTED FOR AS LONG AS SEVERAL
     YEARS.

RISK OF NONDIVERSIFICATION
[FLAG]As  an index  fund,  the Fund will hold the  largest  stocks in its target
index in  approximately  the same percentages as those stocks are represented in
the index. If the target index should become less diversified in the future, the
Fund  similarly  would become less  diversified.  In the unlikely event that the
target index becomes  dominated by just a few companies,  shareholders  would be
subject to the risk that the Fund's performance could be hurt disproportionately
by a decline in the price of just a few stocks.

SECURITY SELECTION

INDEXING METHODS
In seeking to track a particular index, a fund generally uses one of two methods
to select the securities in which it invests.
<PAGE>


                                                                               7

     REPLICATION   METHOD.   Many  stock  funds--but  not  bond  funds--use  the
replication method of indexing. This means that a fund holds each security found
in its target index in about the same  proportions  as  represented in the index
itself.  For example,  if 5% of the S&P 500 Index were made up of the stock of a
specific company, a fund tracking that index would invest about 5% of its assets
in that company. For bond funds, replication is an inefficient and costly method
of  indexing,  since  there is no liquid  market for many of the  corporate  and
agency bonds typically found in a broad bond index.
     STRAIGHT   SAMPLING  METHOD.   Because  it  would  be  very  expensive  and
inefficient to buy and sell all securities held in certain indexes (the Wilshire
5000 Index, for example,  includes more than 7,000 stocks), funds tracking these
larger   indexes   sometimes  use  a  "straight   sampling"   technique.   Using
sophisticated  computer  programs,  a fund  selects,  from the target  index,  a
representative  sample of securities that will resemble the full target index in
terms of key risk  factors.  For stock  funds,  these key risk  factors  include
industry  weightings,  country  weightings,  market  capitalization,  and  other
financial characteristices of stocks.
     Vanguard Calvert Social Index Fund uses the replication  method of indexing
to invest in stocks.

TURNOVER RATE
Generally,  a  passively  managed  fund  sells  securities  only to  respond  to
redemption  requests  or to adjust the number of shares held to reflect a change
in the fund's target index.



- --------------------------------------------------------------------------------
                               PLAIN TALK ABOUT
                                 TURNOVER RATE
Before  investing in a mutual fund,  you should review its turnover  rate.  This
gives an  indication  of how  transaction  costs could affect the fund's  future
returns.  In general,  the greater the volume of buying and selling by the fund,
the greater the impact that brokerage  commissions and other  transaction  costs
will have on its return. Also, funds with high turnover rates may be more likely
to generate  capital gains that must be  distributed to  shareholders  as income
subject to taxes. The average  turnover rate for all passively  managed domestic
equity index funds  investing  in common  stocks is roughly .%; for all domestic
stock  funds,  the  average  turnover  rate is  approximately  .,  according  to
Morningstar, Inc.
- --------------------------------------------------------------------------------


OTHER INVESTMENT POLICIES AND RISKS

The Fund  reserves  the right to  substitute  a different  index for the Calvert
Social Index if the Calvert Social Index is discontinued or for any other reason
determined in good faith by the Fund's Board of Trustees. In such instance,  the
substitute index will measure the same general market as the current index.
     The Fund may invest in foreign  securities to the extent necessary to carry
out its investment strategy of holding all of the stocks that comprise the index
it tracks.
<PAGE>


8

     To match its target  index as closely as  possible,  the Fund  attempts  to
remain  fully  invested in stocks.  To help stay fully  invested,  and to reduce
transaction  costs,  the Fund may invest,  to a limited  extent,  in stock index
futures  and  options  contracts,  warrants,  convertible  securities,  and swap
agreements,  which  are  types of  derivatives.  These  investments  will not be
screened based on social or environmental criteria.
     Losses (or gains) involving futures can sometimes be  substantial--in  part
because a relatively small price movement in a futures contract may result in an
immediate and substantial  loss (or gain) for the Fund.  Similar risks exist for
warrants  (securities  that permit their owners to purchase a specific number of
stock shares at a predetermined price),  convertible securities (securities that
may be exchanged for another  asset),  and swap  agreements  (contracts in which
each  party  agrees  to make  payments  to the  other  based on the  return of a
specified index or asset).
     For  this  reason,  the  Fund  will  not use  futures,  options,  warrants,
convertible  securities,  or swap  agreements  for  speculative  purposes  or as
leveraged investments that magnify the gains or losses of an investment.
     The Fund's  obligation to purchase  securities under futures contracts will
not exceed 20% of its total assets.
 The reasons for which the Fund will invest in futures and options are:
- -    To keep cash on hand to meet  shareholder  redemptions or other needs while
     simulating full investment in stocks.
- -    To reduce the Fund's  transaction costs or add value when these instruments
     are favorably priced.
     Although index funds, by their nature, tend to be tax-efficient  investment
vehicles, the Fund generally is managed without regard to tax ramifications.


- --------------------------------------------------------------------------------
                               PLAIN TALK ABOUT
                                  DERIVATIVES
A derivative is a financial contract whose value is based on (or "derived" from)
a  traditional  security  (such  as a stock  or a  bond),  an  asset  (such as a
commodity like gold), or a market index (such as the S&P 500 Index). Futures and
options are derivatives  that have been trading on regulated  exchanges for more
than two decades.  These  "traditional"  derivatives are standardized  contracts
that can easily be bought and sold,  and whose market values are  determined and
published  daily. It is these  characteristics  that  differentiate  futures and
options from the relatively new types of derivatives. If used for speculation or
as leveraged investments, derivatives can carry considerable risks.
- --------------------------------------------------------------------------------


THE FUND AND VANGUARD

The Fund is a member of The Vanguard  Group, a family of more than 35 investment
companies  with more than 100 funds  holding  assets worth more than $. billion.
All of the  Vanguard  funds  share  in the  expenses  associated  with  business
operations, such as personnel, office space, equipment, and advertising.
     Vanguard  also  provides   marketing   services  to  the  funds.   Although
shareholders do not pay sales commissions or 12b-1  distribution fees, each fund
pays its allocated share of The Vanguard Group's marketing costs.
<PAGE>


                                                                               9



- --------------------------------------------------------------------------------
                               PLAIN TALK ABOUT
                     VANGUARD'S UNIQUE CORPORATE STRUCTURE


The Vanguard Group is truly a MUTUAL mutual fund company. It is owned jointly by
the funds it oversees and thus  indirectly by the  shareholders  in those funds.
Most other mutual funds are operated by for-profit management companies that may
be owned by one person,  by a group of individuals,  or by investors who own the
management  company's stock. By contrast,  Vanguard  provides its services on an
"at-cost"  basis,  and the funds' expense  ratios  reflect only these costs.  No
separate  management  company reaps profits or absorbs losses from operating the
funds.
- --------------------------------------------------------------------------------


INVESTMENT ADVISER

The Vanguard Group (Vanguard), P.O. Box 2600, Valley Forge, PA 19482, founded in
1974,  serves as the Fund's adviser  through its Core  Management  Group.  As of
October 31, 1999,  Vanguard  served as adviser for about $346 billion in assets.
Vanguard  manages  the fund on an at-cost  basis,  subject to the control of the
Trustees and officers of the Fund.
     The Fund has  authorized the adviser to choose brokers or dealers to handle
the purchase and sale of securities  for the Fund, and to get the best available
price and most  favorable  execution  from  these  brokers  with  respect to all
transactions.  Also, the Fund may direct the adviser to use a particular  broker
for certain transactions in exchange for commission rebates or research services
provided to the Fund.


- --------------------------------------------------------------------------------
                               PLAIN TALK ABOUT
                              THE FUND'S ADVISER

The individual primarily responsible for overseeing the Fund's investments is:

GEORGE U. SAUTER,  Managing  Director of Vanguard,  and head of Vanguard's  Core
Management  Group;  has worked in  investment  management  since  1985;  primary
responsibility  for Vanguard's  stock indexing policy and strategy since joining
the company in 1987; has served as the Fund's portfolio manager since inception;
A.B., Dartmouth College; M.B.A., University of Chicago.
- --------------------------------------------------------------------------------

DIVIDENDS, CAPITAL GAINS, AND TAXES

The Fund  distributes to shareholders  virtually all of its net income (interest
and dividends,  less  expenses),  as well as any capital gains realized from the
sale of its holdings.  Distributions  generally occur in December.  In addition,
the Fund may occasionally be required to make  supplemental  dividend or capital
gains distributions at some other time during the year.
     Your  dividend  and  capital  gains  distributions  will be  reinvested  in
additional  Fund  shares  and  accumulate  on a  tax-deferred  basis  if you are
investing through an employer-sponsored retirement or savings plan. You will not
owe taxes on these  distributions until you begin withdrawals from the plan. You
should consult your plan administrator, your plan's Summary Plan Description, or
your tax adviser about the tax consequences of plan withdrawals.
<PAGE>


10


- --------------------------------------------------------------------------------
                               PLAIN TALK ABOUT
                                 DISTRIBUTIONS
As a  shareholder,  you are  entitled  to your share of the fund's  income  from
interest and dividends, and gains from the sale of investments. You receive such
earnings as either an income  dividend or a capital gains  distribution.  Income
dividends come from both the dividends that the fund earns from its holdings and
the  interest it receives  from its money market and bond  investments.  Capital
gains are realized  whenever the fund sells securities for higher prices than it
paid for them. These capital gains are either short-term or long-term, depending
on whether the fund held the  securities  for one year or less, or more than one
year.
- --------------------------------------------------------------------------------


SHARE PRICE

The Fund's share price,  called its net asset value,  or NAV, is calculated each
business day after the close of regular  trading on the New York Stock  Exchange
(the NAV is not  calculated  on  holidays  or other  days when the  Exchange  is
closed).  Net asset  value per share is computed by adding up the total value of
the Fund's  investments  and other assets,  subtracting  any of its  liabilities
(debts),  and then  dividing  the net assets  attributable  to each class by the
number of Fund shares outstanding for each class.


           NET ASSET VALUE = TOTAL ASSETS - LIABILITIES
                         -------------------------------
                          NUMBER OF SHARES OUTSTANDING


     Knowing the daily net asset value is useful to you as a shareholder because
it indicates the current value of your investment. The Fund's NAV, multiplied by
the  number of  shares  you own,  gives you the  dollar  amount  you would  have
received had you sold all of your shares back to the Fund that day.
     A NOTE ON PRICING:  The Fund's  investments  will be priced at their market
value when market  quotations are readily  available.  When these quotations are
not  readily  available,  investments  will  be  priced  at  their  fair  value,
calculated according to procedures adopted by the Fund's Board of Trustees.
     The Fund's  share price can be found  daily in the mutual fund  listings of
most major  newspapers  under the  heading  "Vanguard  Index  Funds."  Different
newspapers use different  abbreviations  of the Fund's name, but the most common
is ..












"Standard & Poor's(R),"  "S&P(R),"  "S&P  500(R),"  "Standard & Poor's 500," and
"500" are trademarks of The McGraw-Hill Companies, Inc.
<PAGE>


                                                                              11


INVESTING WITH VANGUARD

The Fund is an investment  option in your  retirement or savings plan. Your plan
administrator  or your  employee  benefits  office can provide you with detailed
information  on how to  participate in your plan and how to elect the Fund as an
investment option.
- -    If you have any questions about the Fund or Vanguard, including those about
     the Fund's investment objective,  strategies,  or risks, contact Vanguard's
     Participant Services Center, toll-free, at 1-800-523-1188.
- -    If you have questions about your account,  contact your plan  administrator
     or the organization that provides recordkeeping services for your plan.

INVESTMENT OPTIONS AND ALLOCATIONS
Your  plan's  specific  provisions  may  allow  you to  change  your  investment
selections,  the amount of your  contributions,  or how your  contributions  are
allocated  among the  investment  choices  available  to you.  Contact your plan
administrator or employee benefits office for more details.

TRANSACTIONS
Contributions,  exchanges,  or redemptions of the Fund's shares are processed as
soon as they have been received by Vanguard in good order. Good order means that
your request includes complete  information on your contribution,  exchange,  or
redemption, and that Vanguard has received the appropriate assets.
     In all cases, your transaction will be based on the Fund's  next-determined
net asset value after  Vanguard  receives  your  request (or, in the case of new
contributions,  the  next-determined net asset value after Vanguard receives the
order from your plan administrator).  As long as this request is received before
the close of trading on the New York Stock  Exchange,  generally 4 p.m.  Eastern
time, you will receive that day's net asset value.

EXCHANGES
The exchange  privilege (your ability to redeem shares from one fund to purchase
shares of another  fund) may be available to you through your plan.  Although we
make every  effort to maintain  the exchange  privilege,  Vanguard  reserves the
right to revise or terminate this privilege, limit the amount of an exchange, or
reject any exchange,  at any time, without notice.  Because excessive  exchanges
can potentially  disrupt the management of the Fund and increase its transaction
costs,  Vanguard  limits  participant  exchange  activity  to no more  than FOUR
SUBSTANTIVE  "ROUND TRIPS"  THROUGH THE FUND (at least 90 days apart) during any
12-month  period.  A "round  trip" is a redemption  from the Fund  followed by a
purchase back into the Fund.  "Substantive"  means a dollar amount that Vanguard
determines, in its sole discretion, could adversely affect the management of the
Fund.
     Before  making an exchange to or from another fund  available in your plan,
consider the following:
- -    Certain investment options,  particularly funds made up of company stock or
     investment contracts, may be subject to unique restrictions.
- -    Make sure to read that fund's  prospectus.  Contact  Participant  Services,
     toll-free, at 1-800-523-1188 for a copy.
- -    Vanguard can accept exchanges only as permitted by your plan.  Contact your
     plan  administrator for details on the exchange policies that apply to your
     plan.
<PAGE>


12

ACCESSING FUND INFORMATION BY COMPUTER

- --------------------------------------------------------------------------------
VANGUARD ON THE WORLD WIDE WEB www.vanguard.com
Use your personal computer to visit Vanguard's education-oriented website, which
provides  timely news and  information  about  Vanguard  funds and services;  an
online  "university"  that  offers  a  variety  of  mutual  fund  classes;   and
easy-to-use,  interactive  tools to help you  create  your  own  investment  and
retirement strategies.
- --------------------------------------------------------------------------------
<PAGE>

GLOSSARY OF INVESTMENT TERMS


ACTIVE MANAGEMENT
An investment approach that seeks to exceed the average returns of the financial
markets.  Active  managers  rely on research,  market  forecasts,  and their own
judgment and experience in selecting securities to buy and sell.

CAPITAL GAINS DISTRIBUTION
Payment to mutual fund  shareholders of gains realized on securities that a fund
has sold at a profit, minus any realized losses.

CASH RESERVES
Cash deposits,  short-term  bank deposits,  and money market  instruments  which
include U.S.  Treasury bills,  bank  certificates  of deposit (CDs),  repurchase
agreements, commercial paper, and banker's acceptances.

COMMON STOCK
A security  representing  ownership  rights in a  corporation.  A stockholder is
entitled  to share in the  company's  profits,  some of which may be paid out as
dividends.

DIVIDEND INCOME
Payment to  shareholders  of income from  interest or  dividends  generated by a
fund's investments.

EXPENSE RATIO
The  percentage  of a fund's  average net assets used to pay its  expenses.  The
expense ratio  includes  management  fees,  administrative  fees,  and any 12b-1
distribution fees.

INDEX
An unmanaged group of securities whose overall performance is used as a standard
to measure investment performance.

INVESTMENT ADVISER
An  organization  that  makes  the  day-to-day   decisions  regarding  a  fund's
investments.

MUTUAL FUND
An  investment  company  that pools the money of many people and invests it in a
variety of securities in an effort to achieve a specific objective over time.

NET ASSET VALUE (NAV)
The market value of a mutual fund's total assets, minus liabilities,  divided by
the  number of shares  outstanding.  The value of a single  share is called  its
share value or share price.

PASSIVE MANAGEMENT
A low-cost  investment strategy in which a mutual fund attempts to match--rather
than  outperform--a  particular  stock  or bond  market  index.  Also  known  as
indexing.

PRINCIPAL
The amount of your own money you put into an investment.

SECURITIES
Stocks, bonds, money market instruments, and other investment vehicles.

TOTAL RETURN
A percentage change,  over a specified time period, in a mutual fund's net asset
value,  with the ending net asset value adjusted to account for the reinvestment
of all distributions of dividends and capital gains.

VOLATILITY
The  fluctuations  in value of a mutual  fund or other  security.  The greater a
fund's volatility, the wider the fluctuations between its high and low prices.

YIELD
Income (interest or dividends) earned by an investment, expressed as a
percentage of the investment's price.
<PAGE>

[SHIP]
[THE VANGUARD GROUP LOGO]
Institutional Division
Post Office Box 2900
Valley Forge, PA 19482-2900

FOR MORE INFORMATION
If you'd like more information about
Vanguard Calvert Social Index Fund,
the following documents are
available free upon request:

ANNUAL/SEMIANNUAL REPORTS TO
SHAREHOLDERS
Additional information about the
Fund's investments is available in
the Fund's annual and semiannual
reports to shareholders.

STATEMENT OF ADDITIONAL
INFORMATION (SAI)
The SAI provides more detailed
information about the Fund.

The current annual and semiannual
reports and the SAI are
incorporated by reference into
(and are thus legally a part of)
this prospectus.

To receive a free copy of the latest
annual or semiannual report or the
SAI, or to request additional
information about the Fund or other
Vanguard funds, please contact us
as follows:

THE VANGUARD GROUP
PARTICIPANT SERVICES CENTER
P.O. BOX 2900
VALLEY FORGE, PA 19482-2900

TELEPHONE:
1-800-523-1188

TEXT TELEPHONE:
1-800-523-8004

WORLD WIDE WEB:
WWW.VANGUARD.COM

INFORMATION PROVIDED BY THE
SECURITIES AND EXCHANGE
COMMISSION (SEC)
You can review and copy
information about the Fund
(including the SAI) at the SEC's
Public Reference Room in
Washington, DC. To find out more
about this public service, call the
SEC at 1-800-SEC-0330. Reports and
other information about the Fund are
also available on the SEC's website
(www.sec.gov), or you can receive
copies of this information, for a fee,
by writing the Public Reference
Section, Securities and Exchange
Commission, Washington, DC
20549-0102.

Fund's Investment Company Act
file number: 811-1027

(C) 2000 The Vanguard Group, Inc.
All rights reserved.
Vanguard Marketing Corporation,
Distributor.

 .-04/28/2000
<PAGE>

SUBJECT TO COMPLETION
PRELIMINARY PROSPECTUS
DATED FEBRUARY 23, 2000

VANGUARD(R)
CALVERT SOCIAL INDEX
FUND
INSTITUTIONAL SHARES

Prospectus
April 28, 2000

This is the Fund's initial
prospectus, so it contains
no performance data.


INFORMATION   CONTAINED  HEREIN  IS  SUBJECT  TO  COMPLETION  OR  AMENDMENT.   A
REGISTRATION STATEMENT RELATING TO THESE SECURITIES HAS BEEN FILED WITH THE U.S.
SECURITIES AND EXCHANGE  COMMISSION BUT HAS NOT YET BECOME EFFECTIVE.  SHARES OF
VANGUARD  CALVERT  SOCIAL  INDEX FUND MAY NOT BE SOLD,  NOR MAY OFFERS TO BUY BE
ACCEPTED,  PRIOR TO THE TIME THE REGISTRATION STATEMENT BECOMES EFFECTIVE.  THIS
COMMUNICATION  SHALL NOT  CONSTITUTE  AN OFFER TO SELL OR A  SOLICITATION  OF AN
OFFER TO BUY,  NOR  SHALL  THERE BE ANY SALE OF THESE  SECURITIES  IN A STATE IN
WHICH SUCH OFFER, SOLICITATION,  OR SALE WOULD BE UNLAWFUL PRIOR TO REGISTRATION
OR QUALIFICATION UNDER THE SECURITIES LAW OF THE STATE.

[A MEMBER OF
THE VANGUARD GROUP LOGO]

<PAGE>

VANGUARD CALVERT SOCIAL INDEX FUND
Prospectus
April 28, 2000

A Stock Index Mutual Fund

- --------------------------------------------------------------------------------
CONTENTS
- --------------------------------------------------------------------------------
 .  FUND PROFILE                         .  SHARE PRICE
 .  ADDITIONAL INFORMATION               .  INVESTING WITH VANGUARD
 .  AN INTRODUCTION TO INDEX FUNDS        .  SERVICES AND ACCOUNT FEATURES
 .  A WORD ABOUT RISK                     .  TYPES OF ACCOUNTS
 .  WHO SHOULD INVEST                     .  BUYING SHARES
 .  PRIMARY INVESTMENT STRATEGIES         .  REDEEMING SHARES
 .  THE FUND AND VANGUARD                 .  TRANSFERRING REGISTRATION
 .  INVESTMENT ADVISER                    .  FUND AND ACCOUNT UPDATES
 .  DIVIDENDS, CAPITAL GAINS, AND TAXES  GLOSSARY (inside back cover)
- --------------------------------------------------------------------------------


- --------------------------------------------------------------------------------
WHY READING THIS PROSPECTUS IS IMPORTANT

This  prospectus  explains the  objective,  risks,  and  strategies  of Vanguard
Calvert Social Index Fund Institutional  Shares. To highlight terms and concepts
important  to  mutual  fund  investors,   we  have  provided  "Plain  Talk/(R)/"
explanations  along  the way.  Reading  the  prospectus  will help you to decide
whether the Fund is the right  investment  for you. We suggest  that you keep it
for future reference.
- --------------------------------------------------------------------------------

- --------------------------------------------------------------------------------
IMPORTANT NOTE
Vanguard  Calvert  Social  Index  Fund  offers two  separate  classes of shares:
Investor and  Institutional.  This  prospectus  offers the Fund's  Institutional
Shares,  which have an  investment  minimum of $10 million and are  intended for
investors who generally do not require special  employee benefit  services.  The
Fund's Investor Shares have an investment  minimium of $3,000 ($1,000 for IRAs),
and are available through separate  prospectuses  (one for individual  investors
and one for participants in employer-sponsored retirement or savings plans).

Note that the Fund's  separate  share  classes  have  different  expenses;  as a
result, their investment performances will vary.
- --------------------------------------------------------------------------------









NEITHER  THE  SECURITIES  AND  EXCHANGE  COMMISSION  NOR  ANY  STATE  SECURITIES
COMMISSION HAS APPROVED OR  DISAPPROVED  OF THESE  SECURITIES OR PASSED UPON THE
ACCURACY OR ADEQUACY OF THIS PROSPECTUS. ANY REPRESENTATION TO THE CONTRARY IS A
CRIMINAL OFFENSE.
<PAGE>


                                                                               1

FUND PROFILE

The following  profile  summarizes key features of Vanguard Calvert Social Index
Fund Institutional Shares.

INVESTMENT OBJECTIVE
The Fund seeks to track the  performance of a benchmark  index that measures the
investment return of large- and mid-capitalization stocks.

INVESTMENT STRATEGIES
The Fund employs a passive management strategy designed to track the performance
of the Calvert Social Index.  The Index is composed of large- and mid-cap stocks
that have been  screened for certain  social and  environmental  criteria by the
index sponsor,  which is independent of Vanguard. The Fund invests in the stocks
that comprise the Index.

PRIMARY RISKS
THE FUND'S TOTAL RETURN,  LIKE STOCK PRICES  GENERALLY,  WILL FLUCTUATE WITHIN A
WIDE  RANGE,  SO AN INVESTOR  COULD LOSE MONEY OVER SHORT OR EVEN LONG  PERIODS.
Stock markets tend to move in cycles,  with periods of rising prices and periods
of falling prices. The Fund is also subject to:
- -    Investment  style risk,  which is the chance that  returns  from large- and
     mid-cap  stocks  generally,  or from stocks  included in the Calvert Social
     Index  specifically,  will trail  returns  from other asset  classes or the
     overall stock market.


- --------------------------------------------------------------------------------
                               PLAIN TALK ABOUT
                                 FUND EXPENSES
All mutual funds have operating  expenses.  These  expenses,  which are deducted
from a fund's gross  income,  are expressed as a percentage of the net assets of
the fund. We expect Vanguard  Calvert Social Index Fund's  Institutional  Shares
expense ratio for the current  fiscal year to be .%, or $. per $1,000 of average
net assets.  The average multi-cap mutual fund had expenses in 1999 of .%, or $.
per $1,000 of average net assets,  (derived  from data  provided by Lipper Inc.,
which reports on the mutual fund industry).  Management expenses,  which are one
part of operating  expenses,  include investment  advisory fees as well as other
costs of managing a fund--such as account  maintenance,  reporting,  accounting,
legal, and other administrative expenses.
- --------------------------------------------------------------------------------


FEES AND EXPENSES
The following table describes the fees and expenses you would pay if you buy and
hold  Institutional  Shares of the Fund.  The  expenses  shown under Annual Fund
Operating Expenses are based upon estimated amounts for the current fiscal year.
The Fund has no  operating  history,  and  actual  operating  expenses  could be
different.
<PAGE>


2

      SHAREHOLDER FEES (fees paid directly from your investment)
      Sales Charge (Load) Imposed on Purchases:               None
      Sales Charge (Load) Imposed on Reinvested Dividends:    None
      Redemption Fee:                                         None
      Exchange Fee:                                           None


      ANNUAL FUND OPERATING EXPENSES (expenses deducted from the
      Fund's assets)
      Management Expenses:                                      .%
      12b-1 Distribution Fee:                                 None
      Other Expenses:                                           .%
       TOTAL ANNUAL FUND OPERATING EXPENSES:                 0.15%


     The following example is intended to help you compare the cost of investing
in the Fund with the cost of investing in other mutual funds. It illustrates the
hypothetical  expenses that you would incur over one-year and three-year periods
if you invest $10,000 in the Fund's  Institutional  Shares. This example assumes
that the Fund provides a return of 5% a year, and that operating  expenses match
our estimates for the Fund's first year of operations.The  results apply whether
or not you redeem your investment at the end of each period.


                            ------------------------
                             1 YEAR     3 YEARS
                            ------------------------
                                $.         $.
                            ------------------------


     THIS  EXAMPLE  SHOULD NOT BE  CONSIDERED  TO REPRESENT  ACTUAL  EXPENSES OR
PERFORMANCE  FROM THE PAST OR FOR THE  FUTURE.  ACTUAL  FUTURE  EXPENSES  MAY BE
HIGHER OR LOWER THAN THOSE SHOWN.



- --------------------------------------------------------------------------------
ADDITIONAL INFORMATION
DIVIDENDS AND CAPITAL GAINS              NEWSPAPER ABBREVIATION
Distributed annually in December         .

INVESTMENT ADVISERS                      VANGUARD FUND NUMBER
The Vanguard Group, Valley Forge, Pa.,   .
since inception
                                         CUSIP NUMBER
INCEPTION DATE                           .
May 8, 2000
                                         TICKER SYMBOL
SUITABLE FOR IRAS                        .
Yes

MINIMUM INITIAL INVESTMENT
$10 million
- --------------------------------------------------------------------------------



AN INTRODUCTION TO INDEX FUNDS

WHAT IS INDEXING?
An index is an unmanaged group of securities  whose overall  performance is used
as a standard to measure the investment  performance of a particular  market. An
index (or "passively managed") fund tries to track, as closely as possible,  the
performance of an established  target index.  The fund does this by holding all,
or a representative sample, of the securities that comprise the index.


                                                                               3

     Stock index  funds may seek to track  indexes  that hold a certain  type of
stock--such as growth or value,  small-cap or large-cap,  or those from just one
industry--or  they may seek to track  indexes that consist of a broader range of
stocks--for example the entire U.S. stock market.
     Index funds do not have active managers,  who buy and sell securities based
on research and analysis in an attempt to  outperform a particular  benchmark or
the market as a whole.  Rather,  index funds  simply  attempt to mirror what the
target index does, for better or worse.

WHY INVEST IN INDEX FUNDS?
Index funds appeal to many investors for a number of reasons:
- -    Variety of  investments.  Vanguard index funds  generally  invest in a wide
     variety of companies and industries.
- -    Relative consistency.  Because they seek to track market benchmarks,  index
     funds by  definition  will not  perform  dramatically  better or worse than
     their target indexes.
- -    Low cost.  Index  funds do not have  many of the  expenses  of an  actively
     managed fund, in addition,  they keep trading  activity--and thus brokerage
     commissions--to a minimum.
- -    Low  realization  of capital gains.  Because an index fund typically  sells
     securities only to respond to redemption requests or to adjust its holdings
     to reflect a change in its target index, the fund's turnover rate--and thus
     its  realization of taxable capital  gains--is  usually much lower than the
     average mutual fund.


- --------------------------------------------------------------------------------
                               PLAIN TALK ABOUT
                            THE COSTS OF INVESTING
Costs are an important  consideration in choosing a mutual fund.  That's because
you, as a shareholder,  pay the costs of operating a fund,  plus any transaction
costs  associated with the fund's buying and selling of securities.  These costs
can erode a substantial  portion of the gross income or capital  appreciation  a
fund achieves. Even seemingly small differences in expenses can, over time, have
a dramatic effect on a fund's performance.
- --------------------------------------------------------------------------------



     KEEP IN MIND THAT AN INDEX  FUND HAS  OPERATING  EXPENSES  AND  TRANSACTION
COSTS;  A MARKET INDEX DOES NOT.  THEREFORE,  AN INDEX  FUND--WHILE  EXPECTED TO
TRACK ITS TARGET INDEX AS CLOSELY AS POSSIBLE--WILL TYPICALLY BE UNABLE TO MATCH
THE PERFORMANCE OF THE INDEX EXACTLY.
<PAGE>


4



================================================================================
A WORD ABOUT RISK
This  prospectus  describes  risks you would  face as an  investor  in  Vanguard
Calvert  Social  Index  Fund.  It is  important  to keep in mind one of the main
axioms of  investing:  The  higher  the risk of losing  money,  the  higher  the
potential reward. The reverse,  also, is generally true: The lower the risk, the
lower the  potential  reward.  As you consider an  investment  in the Fund,  you
should also take into account your personal tolerance for the daily fluctuations
of the stock market.
     Look for this [FLAG] symbol  throughout the prospectus.  It is used to mark
detailed  information  about  each  type of risk that you  would  confront  as a
shareholder of the Fund.
================================================================================


WHO SHOULD INVEST

The Fund may be a suitable investment for you if:
- -    You wish to add a fund that invests in large- and mid-capitalization stocks
     to your existing  holdings,  which could include other stock investments as
     well as bond, money market, and tax-exempt investments.
- -    You seek growth of capital over the long-term--at least five years.
- -    You want a fund that considers social and  environmental  issues as part of
     its investment program.

Some  investors  try to profit from a strategy  called  market-timing--switching
money into  investments  when they expect  prices to rise,  and taking money out
when they expect  prices to fall.  As money is shifted in and out, a fund incurs
expenses  for buying and selling  securities.  These costs are borne by all fund
shareholders,  including the long-term  investors who do not generate the costs.
This is why all  Vanguard  funds have  adopted  special  policies to  discourage
short-term trading. Specifically:
- -    Each   Vanguard   fund   reserves   the  right  to  reject   any   purchase
     request--including  exchanges from other Vangaurd funds--that it regards as
     disruptive  to  efficient  portfolio  management.  The  fund  may  reject a
     purchase  request  because of the timing of the  investment or because of a
     history of excessive trading by the investor.
- -    Each  Vanguard  fund (except the money market  funds)  limits the number of
     times that an investor can exchange into and out of the fund.
- -    Each Vanguard fund reserves the right to stop offering shares at any time.
- -    Vanguard's U.S. Stock Index Funds,  International  Stock Index Funds,  REIT
     Index Fund,  Balanced  Index Fund,  and Growth and Income Fund generally do
     NOT accept  exchanges  by  telephone  or fax,  or  online.  (IRAs and other
     retirement accounts are not subject to this rule.)
- -    Certain  Vanguard  funds  charge   transaction  fees  on  purchases  and/or
     redemptions of their shares.
See the INVESTING WITH VANGUARD  section of this  prospectus for further details
on Vanguard's transaction policies.

     THE VANGUARD FUNDS DO NOT PERMIT MARKET-TIMING. DO NOT INVEST WITH VANGUARD
IF YOU ARE A MARKET TIMER.
<PAGE>


                                                                               5

PRIMARY INVESTMENT STRATEGIES
This section explains the strategies that the investment adviser uses in pursuit
of the Fund's investment objective.  It also explains how the adviser implements
these strategies.  In addition,  this section discusses important risks faced by
investors  in the Fund.  The Board of Trustees  oversees the  management  of the
Fund, and may change the investment strategies in the interest of shareholders.


- --------------------------------------------------------------------------------
                               PLAIN TALK ABOUT
                             CALVERT SOCIAL INDEX
The Calvert Social Index is maintained by Calvert Group of Bethesda, Maryland, a
leading  organization in the world of social  investing.  Calvert screens stocks
from  approximately  1,000 of the  largest  companies  in the  United  States by
analyzing each company's record and policies on: environmental issues; workplace
issues;  product safety and impact;  international  operations and human rights;
and weapons contracting.

Calvert  excludes  from the index any  companies  that,  in  Calvert's  opinion,
violate fair labor or equal  opportunity  standards  as well as those  companies
involved with tobacco, alcohol,  gambling, or nuclear power. Companies that pass
Calvert's   screenings  process  are  represented  in  the  index  on  a  market
capitalization-weighted basis.

For further  information about the Calvert Social Index,  please visit Calvert's
web site, at www.calvert.com or contact Calvert at 1-800-368-2745.
- --------------------------------------------------------------------------------


- --------------------------------------------------------------------------------
                               PLAIN TALK ABOUT
                         GROWTH FUNDS AND VALUE FUNDS
Growth  investing  and value  investing  are two styles  employed  by stock fund
managers.   Growth  funds  generally   focus  on  companies   believed  to  have
above-average  potential  for growth in revenue  and  earnings.  Reflecting  the
market's high  expectations for superior growth,  such stocks typically have low
dividend  yields  and  above-average  prices in  relation  to such  measures  as
revenue,  earnings,  and book value.  Value funds generally  emphasize stocks of
companies  from which the market does not expect  strong  growth.  The prices of
value  stocks  typically  are  below-average  in  comparison  to such factors as
earnings and book value, and these stocks typically pay  above-average  dividend
yields.  Growth and value stocks have, in the past,  produced similar  long-term
returns,  though each  category has periods when it  outperforms  the other.
- --------------------------------------------------------------------------------


<PAGE>


6

MARKET EXPOSURE


[FLAG] THE FUND IS SUBJECT TO STOCK MARKET RISK,  WHICH IS THE CHANCE THAT STOCK
     PRICES OVERALL WILL DECLINE OVER SHORT OR EVEN LONG PERIODS.  STOCK MARKETS
     TEND TO MOVE IN  CYCLES,  WITH  PERIODS  OF RISING  PRICES  AND  PERIODS OF
     FALLING PRICES.

     To illustrate the volatility of stock prices, the following table shows the
best,  worst,  and average total returns for the U.S.  stock market over various
periods as measured by the Standard & Poor's 500 Index,  a widely used barometer
of market  activity.  (Total returns  consist of dividend  income plus change in
market  price.)  Note that the returns  shown do not include the costs of buying
and selling  stocks or other  expenses  that a real-world  investment  portfolio
would  incur.  Note,  also,  that the gap between best and worst tends to narrow
over the long term.



- --------------------------------------------------------------------------------
                      U.S. STOCK MARKET RETURNS (1926-1999)
- --------------------------------------------------------------------------------
                 1 YEAR       5 YEARS        10 YEARS       20 YEARS
- --------------------------------------------------------------------------------
Best              54.2%        28.6%           19.9%          17.9%
Worst            -43.1        -12.4            -0.9            3.1
Average           13.2         11.0            11.1           11.1
- --------------------------------------------------------------------------------

     The table  covers all of the 1-, 5-,  10-,  and 20-year  periods  from 1926
through 1999. You can see, for example,  that while the average return on stocks
for all of the 5-year periods was 11.0%,  returns for individual  5-year periods
ranged  from a -12.4%  average  (from  1928  through  1932) to 28.6%  (from 1995
through 1999).  These average returns reflect past performance on common stocks;
you should not regard them as an  indication  of future  returns from either the
stock market as a whole or this Fund in particular.



- --------------------------------------------------------------------------------
                               PLAIN TALK ABOUT
                   LARGE-CAP, MID-CAP, AND SMALL-CAP STOCKS
Stocks  of  publicly  traded   companies--and   mutual  funds  that  hold  these
stocks--can be classified by the  companies'  market value,  or  capitalization.
Market  capitalization  changes over time, and there is no "official" definition
of the boundaries of large-,  mid-,  and small-cap  stocks.  Vanguard  generally
defines  large-capitalization  (large-cap)  funds as  those  holding  stocks  of
companies  whose  outstanding  shares have a market value exceeding $12 billion;
mid-cap funds as those holding  stocks of companies  with a market value between
$1 billion and $12  billion;  and  small-cap  funds as those  typically  holding
stocks  of  companies  with a market  value of less  than $1  billion.  Vanguard
periodically reassesses these classifications.
- --------------------------------------------------------------------------------



[FLAG] THE FUND IS ALSO SUBJECT TO  INVESTMENT  STYLE RISK,  WHICH IS THE CHANCE
     THAT RETURNS FROM LARGE- AND  MID-CAPITALIZATION  STOCKS WILL TRAIL RETURNS
     FROM OTHER ASSET CLASSES OR THE OVERALL  STOCK  MARKET.  EACH TYPE OF STOCK
     TENDS TO GO THROUGH CYCLES OF DOING BETTER--OR WORSE--THAN COMMON STOCKS IN
     GENERAL.  THESE PERIODS  HAVE,  IN THE PAST,  LASTED FOR AS LONG AS SEVERAL
     YEARS.
<PAGE>


                                                                               7

RISK OF NONDIVERSIFICATION

[FLAG] As an index  fund,  the Fund will hold the  largest  stocks in its target
index in  approximately  the same percentages as those stocks are represented in
the index. If the target index should become less diversified in the future, the
Fund  similarly  would become less  diversified.  In the unlikely event that the
target index becomes  dominated by just a few companies,  shareholders  would be
subject to the risk that the Fund's performance could be hurt disproportionately
by a decline in the price of just a few stocks.

SECURITY SELECTION

INDEXING METHODS
In seeking to track a particular index, a fund generally uses one of two methods
to select the securities in which it invests.
     REPLICATION   METHOD.   Many  stock  funds--but  not  bond  funds--use  the
replication method of indexing. This means that a fund holds each security found
in its target index in about the same  proportions  as  represented in the index
itself.  For example,  if 5% of the S&P 500 Index were made up of the stock of a
specific company, a fund tracking that index would invest about 5% of its assets
in that company. For bond funds, replication is an inefficient and costly method
of  indexing,  since  there is no liquid  market for many of the  corporate  and
agency bonds typically found in a broad bond index.
     STRAIGHT   SAMPLING  METHOD.   Because  it  would  be  very  expensive  and
inefficient to buy and sell all securities held in certain indexes (the Wilshire
5000 Index, for example,  includes more than 7,000 stocks), funds tracking these
larger   indexes   sometimes  use  a  "straight   sampling"   technique.   Using
sophisticated  computer  programs,  a fund  selects,  from the target  index,  a
representative  sample of securities that will resemble the full target index in
terms of key risk  factors.  For stock  funds,  these key risk  factors  include
industry  weightings,  country  weightings,  market  capitalization,  and  other
financial characteristices of stocks.
     Vanguard Calvert Social Index Fund uses the replication  method of indexing
to invest in stocks.

TURNOVER RATE
Generally,  a  passively  managed  fund  sells  securities  only to  respond  to
redemption  requests  or to adjust the number of shares held to reflect a change
in the fund's target index.
<PAGE>


8


- --------------------------------------------------------------------------------
                               PLAIN TALK ABOUT
                                 TURNOVER RATE
Before  investing in a mutual fund,  you should review its turnover  rate.  This
gives an  indication  of how  transaction  costs could affect the fund's  future
returns.  In general,  the greater the volume of buying and selling by the fund,
the greater the impact that brokerage  commissions and other  transaction  costs
will have on its return. Also, funds with high turnover rates may be more likely
to generate  capital gains that must be  distributed to  shareholders  as income
subject to taxes. The average  turnover rate for all passively  managed domestic
equity index funds  investing  in common  stocks is roughly .%; for all domestic
stock  funds,  the  average  turnover  rate is  approximately  .,  according  to
Morningstar, Inc.
- --------------------------------------------------------------------------------


OTHER INVESTMENT POLICIES AND RISKS
The Fund  reserves  the right to  substitute  a different  index for the Calvert
Social Index if the Calvert Social Index is discontinued or for any other reason
determined in good faith by the Fund's Board of Trustees. In such instance,  the
substitute index will measure the same general market as the current index.
     The Fund may invest in foreign  securities to the extent necessary to carry
out its investment strategy of holding all of the stocks that comprise the index
it tracks.
     To match its target  index as closely as  possible,  the Fund  attempts  to
remain  fully  invested in stocks.  To help stay fully  invested,  and to reduce
transaction  costs,  the Fund may invest,  to a limited  extent,  in stock index
futures  and  options  contracts,  warrants,  convertible  securities,  and swap
agreements,  which  are  types of  derivatives.  These  investments  will not be
screened based on social or environmental criteria.
     Losses (or gains) involving futures can sometimes be  substantial--in  part
because a relatively small price movement in a futures contract may result in an
immediate and substantial  loss (or gain) for the Fund.  Similar risks exist for
warrants  (securities  that permit their owners to purchase a specific number of
stock shares at a predetermined price),  convertible securities (securities that
may be exchanged for another  asset),  and swap  agreements  (contracts in which
each  party  agrees  to make  payments  to the  other  based on the  return of a
specified index or asset).
     For  this  reason,  the  Fund  will  not use  futures,  options,  warrants,
convertible  securities,  or swap  agreements  for  speculative  purposes  or as
leveraged investments that magnify the gains or losses of an investment.
     The Fund's  obligation to purchase  securities under futures contracts will
not exceed 20% of its total assets.
     The reasons for which the Fund will invest in futures and options are:
- -    To keep cash on hand to meet  shareholder  redemptions or other needs while
     simulating full investment in stocks.
- -    To reduce the Fund's  transaction costs or add value when these instruments
     are favorably priced.
     Although index funds, by their nature, tend to be tax-efficient  investment
vehicles, the Fund generally is managed without regard to tax ramifications.
<PAGE>


9


- --------------------------------------------------------------------------------
                               PLAIN TALK ABOUT
                                  DERIVATIVES
A derivative is a financial contract whose value is based on (or "derived" from)
a  traditional  security  (such  as a stock  or a  bond),  an  asset  (such as a
commodity like gold), or a market index (such as the S&P 500 Index). Futures and
options are derivatives  that have been trading on regulated  exchanges for more
than two decades.  These  "traditional"  derivatives are standardized  contracts
that can easily be bought and sold,  and whose market values are  determined and
published  daily. It is these  characteristics  that  differentiate  futures and
options from the relatively new types of derivatives. If used for speculation or
as leveraged investments, derivatives can carry considerable risks.
- --------------------------------------------------------------------------------



THE FUND AND VANGUARD

The Fund is a member of The Vanguard  Group, a family of more than 35 investment
companies  with more than 100 funds  holding  assets worth more than $. billion.
All of the  Vanguard  funds  share  in the  expenses  associated  with  business
operations, such as personnel, office space, equipment, and advertising.
     Vanguard  also  provides   marketing   services  to  the  funds.   Although
shareholders do not pay sales commissions or 12b-1  distribution fees, each fund
pays its allocated share of The Vanguard Group's marketing costs.



- --------------------------------------------------------------------------------
                               PLAIN TALK ABOUT
                     VANGUARD'S UNIQUE CORPORATE STRUCTURE
The Vanguard Group is truly a MUTUAL mutual fund company. It is owned jointly by
the funds it oversees and thus  indirectly by the  shareholders  in those funds.
Most other mutual funds are operated by for-profit management companies that may
be owned by one person,  by a group of individuals,  or by investors who own the
management  company's stock. By contrast,  Vanguard  provides its services on an
"at-cost"  basis,  and the funds' expense  ratios  reflect only these costs.  No
separate  management  company reaps profits or absorbs losses from operating the
funds.
- --------------------------------------------------------------------------------

INVESTMENT ADVISER
The Vanguard Group (Vanguard), P.O. Box 2600, Valley Forge, PA 19482, founded in
1974,  serves as the Fund's adviser  through its Core  Management  Group.  As of
October 31, 1999,  Vanguard  served as adviser for about $346 billion in assets.
Vanguard  manages  the fund on an at-cost  basis,  subject to the control of the
Trustees and officers of the Fund.
     The Fund has  authorized the adviser to choose brokers or dealers to handle
the purchase and sale of securities  for the Fund, and to get the best available
price and most  favorable  execution  from  these  brokers  with  respect to all
transactions.  Also, the Fund may direct the adviser to use a particular  broker
for certain transactions in exchange for commission rebates or research services
provided to the Fund.
<PAGE>


10


- --------------------------------------------------------------------------------
                               PLAIN TALK ABOUT
                              THE FUND'S ADVISER
The individual primarily responsible for overseeing the Fund's investments is:

GEORGE U. SAUTER,  Managing  Director of Vanguard,  and head of Vanguard's  Core
Management  Group;  has worked in  investment  management  since  1985;  primary
responsibility  for Vanguard's  stock indexing policy and strategy since joining
the company in 1987; has served as the Fund's portfolio manager since inception;
A.B., Dartmouth College; M.B.A., University of Chicago.
- --------------------------------------------------------------------------------




DIVIDENDS, CAPITAL GAINS, AND TAXES

FUND DISTRIBUTIONS

The Fund  distributes to shareholders  virtually all of its net income (interest
and dividends,  less  expenses),  as well as any capital gains realized from the
sale of its holdings.  Distributions  generally occur in December.  In addition,
the Fund may occasionally be required to make  supplemental  dividend or capital
gains  distributions  at some  other  time  during  the  year.  You can  receive
distributions of income dividends or capital gains in cash, or you can have them
automatically reinvested in more shares of the Fund.

BASIC TAX POINTS

Vanguard will send you a statement  each year showing the tax status of all your
distributions.  In addition,  taxable investors should be aware of the following
basic tax points:
- -    Distributions  are taxable to you whether or not you reinvest these amounts
     in additional Fund shares.
- -    Distributions   declared  in  December--if  paid  to  you  by  the  end  of
     January--are taxable as if received in December.
- -    Any dividends and short-term  capital gains that you receive are taxable to
     you as ordinary income for federal income tax purposes.
- -    Any  distributions  of net  long-term  capital  gains are taxable to you as
     long-term capital gains for federal income tax purposes, no matter how long
     you've owned shares in the Fund.
- -    Capital gains  distributions  may vary  considerably from year to year as a
     result of the Fund's normal investment activities and cash flows.
- -    A sale or exchange of Fund shares is a taxable  event.  This means that you
     may have a capital gain to report as income, or a capital loss to report as
     a deduction, when you complete your federal income tax return.
- -    State and local  income  taxes may apply to any  dividend or capital  gains
     distributions that you receive, as well as to your gains or losses from any
     sale or exchange of Fund shares.

GENERAL INFORMATION

BACKUP  WITHHOLDING.   By  law,  Vanguard  must  withhold  31%  of  any  taxable
distributions  or  redemptions  from your  account if you do not provide us with
your  correct  taxpayer  identification  number and certify  that it is correct.
Similarly,  Vanguard  must withhold from your account if the IRS instructs us to
do so.
FOREIGN  INVESTORS.  The Vanguard funds  generally do not offer their shares for
sale outside of the United States.  Foreign  investors should be aware that U.S.
withholding and estate taxes may apply to any investments in Vanguard funds.
<PAGE>


                                                                              11

INVALID  ADDRESSES.  If a dividend or capital gains distribution check mailed to
your address of record is returned as undeliverable, Vanguard will automatically
reinvest  all future  distributions  until you  provide us with a valid  mailing
address.
TAX CONSEQUENCES.  This prospectus provides general tax information only. If you
are investing through a tax-deferred retirement account, such as an IRA, special
tax rules apply. Please consult your tax adviser for detailed  information about
a fund's tax consequences for you.


- --------------------------------------------------------------------------------
                               PLAIN TALK ABOUT
                                 DISTRIBUTIONS
As a  shareholder,  you are  entitled  to your share of the fund's  income  from
interest and dividends, and gains from the sale of investments. You receive such
earnings as either an income  dividend or a capital gains  distribution.  Income
dividends come from both the dividends that the fund earns from its holdings and
the  interest it receives  from its money market and bond  investments.  Capital
gains are realized  whenever the fund sells securities for higher prices than it
paid for them. These capital gains are either short-term or long-term, depending
on whether the fund held the  securities  for one year or less, or more than one
year.
- --------------------------------------------------------------------------------


- --------------------------------------------------------------------------------
                               PLAIN TALK ABOUT
                              "BUYING A DIVIDEND"
Unless you are investing through a tax-deferred  retirement  account (such as an
IRA),  it is not to your  advantage  to buy shares of a fund  shortly  before it
makes a  distribution,  because  doing so can cost you money in  taxes.  This is
known as "buying a dividend."  For example:  on December 15, you invest  $5,000,
buying 250 shares for $20 each. If the fund pays a distribution  of $1 per share
on December 16, its share price would drop to $19 (not counting  market change).
You still have only $5,000 (250 shares x $19 = $4,750 in share  value,  plus 250
shares x $1 = $250 in  distributions),  but you owe tax on the $250 distribution
you  received--even  if you  reinvest  it in more  shares.  To avoid  "buying  a
dividend," check a fund's distribution schedule before you invest.
- --------------------------------------------------------------------------------


SHARE PRICE

The Fund's share price,  called its net asset value,  or NAV, is calculated each
business day after the close of trading on the New York Stock  Exchange (the NAV
is not  calculated  on holidays or other days when the Exchange is closed).  Net
asset  value per share is  computed  by adding up the total  value of the Fund's
investments and other assets,  subtracting any of its liabilities  (debts),  and
then  dividing the net assets  attributable  to each class by the number of Fund
shares outstanding for each class.



          NET ASSET VALUE = TOTAL ASSETS - LIABILITIES
                         -------------------------------
                          NUMBER OF SHARES OUTSTANDING


     Knowing the daily net asset value is useful to you as a shareholder because
it indicates the current value of your investment. The Fund's NAV, multiplied by
the number of shares
<PAGE>


12

you own, gives you the dollar amount you would have received had you sold all of
your shares back to the Fund that day.
     A NOTE ON PRICING:  The Fund's  investments  will be priced at their market
value when market  quotations are readily  available.  When these quotations are
not  readily  available,  investments  will  be  priced  at  their  fair  value,
calculated according to procedures adopted by the Fund's Board of Trustees.
     The Fund's  share price can be found  daily in the mutual fund  listings of
most major  newspapers  under the  heading  "Vanguard  Index  Funds."  Different
newspapers use different  abbreviations  of the Fund's name, but the most common
is ..






































"Standard & Poor's(R),"  "S&P(R),"  "S&P  500(R),"  "Standard & Poor's 500," and
"500" are trademarks of The McGraw-Hill Companies, Inc.
<PAGE>


                                                                              13



- --------------------------------------------------------------------------------
 INVESTING WITH VANGUARD

Are you looking for the most  convenient  way to open or add money to a Vanguard
account? Obtain instant access to fund information?
     Vanguard  can help.  Our goal is to make it easy and pleasant for you to do
business with us.
     The following  sections of the prospectus briefly explain the many services
we offer.  Booklets providing detailed information are available on the services
marked with a [BOOKLET]. Please call us to request copies.
- --------------------------------------------------------------------------------


SERVICES AND ACCOUNT FEATURES

Vanguard  offers many  services that make it convenient to buy, sell or exchange
shares, or to obtain fund or account information.
- --------------------------------------------------------------------------------
TELEPHONE REDEMPTIONS (SALES AND EXCHANGES)
Automatically set up for this Fund unless you notify us otherwise.
- --------------------------------------------------------------------------------
VANGUARD(R) AUTOMATIC EXCHANGE SERVICE [BOOKLET]
Automatic  method for  moving a fixed  amount of money  from one  Vanguard  fund
account to another.
- --------------------------------------------------------------------------------
VANGUARD TELE-ACCOUNT(R) 1-800-662-6273 (ON-BOARD)[BOOKLET]
Toll-free  24-hour access to Vanguard fund and account  information--as  well as
some  transactions--by  using any touch-tone phone.  Tele-Account provides total
return,  share price, price change, and yield quotations for all Vanguard funds;
gives your account balances and history (e.g., last transaction, latest dividend
distribution);  and  allows  you to sell or  exchange  shares  to and from  most
Vanguard funds.
- --------------------------------------------------------------------------------
ACCESS VANGUARD(TM) www.vanguard.com [COMPUTER]
You can use your  personal  computer to perform  certain  transactions  for most
Vanguard  funds by accessing our website.  To establish  this service,  you must
register  through our website.  We will then mail you an account access password
that  allows  you  to  process  the  following   financial  and   administrative
transactions online:
- -    Open a new account.*
- -    Buy, sell, or exchange shares of most funds.
- -    Change your name/address.
- -    Add/change fund options  (including  dividend options,  bank  instructions,
     checkwriting,  and Vanguard Automatic Exchange Service). (Some restrictions
     may apply.) Please call our Client Services Department for assistance.

*Only current Vanguard shareholders can open a new account online, by exchanging
shares from other existing Vanguard accounts.
- --------------------------------------------------------------------------------
SERVICES FOR CLIENTS OF VANGUARD'S INSTITUTIONAL DIVISION: 1-888-809-8102
Vanguard's  Institutional  Division offers a variety of specialized services for
large  institutional   investors,   including  the  ability  to  effect  account
transactions through private electronic networks and third-party recordkeepers.
- --------------------------------------------------------------------------------
<PAGE>


14

TYPES OF ACCOUNTS

Individuals and institutions can establish a variety of accounts with Vanguard.
- --------------------------------------------------------------------------------
FOR ONE OR MORE PEOPLE
Open an account in the name of one (individual) or more (joint tenants) people.
- --------------------------------------------------------------------------------
FOR HOLDING PERSONAL TRUST ASSETS [BOOKLET]
Invest assets held in an existing personal trust.
- --------------------------------------------------------------------------------
FOR AN ORGANIZATION [BOOKLET]
Open an account as a corporation,  partnership,  endowment, foundation, or other
entity.
- --------------------------------------------------------------------------------

- --------------------------------------------------------------------------------
A NOTE ON INVESTING WITH VANGUARD THROUGH OTHER FIRMS
You may purchase or sell Fund shares through a financial  intermediary such as a
bank,  broker,  or investment  adviser.  If you invest with Vanguard  through an
intermediary,  please read that firm's program  materials  carefully to learn of
any  special  rules  that may apply.  For  example,  special  terms may apply to
additional service features, fees, or other policies.  Consult your intermediary
to determine when your order will be priced.
- --------------------------------------------------------------------------------


BUYING SHARES

You buy your shares at the Fund's next-determined net asset value after Vanguard
receives your request.  As long as your request is received  before the close of
trading on the New York Stock Exchange,  generally 4 p.m. Eastern time, you will
buy your shares at that day's net asset value.  You may convert  Investor Shares
of the Fund into Institutional Shares provided that you meet the minimum initial
investment requirements for Institutional Shares.
- --------------------------------------------------------------------------------
MINIMUM INVESTMENT TO . . .
open a new account
$10 million

add to an existing account
$100 by mail or exchange; $1,000 by wire.
- --------------------------------------------------------------------------------
BY WIRE TO OPEN A NEW ACCOUNT OR ADD TO AN EXISTING ACCOUNT [WIRE]
Call your assigned Service Assoicate to arrange your wire transaction.

Wire to:
FRB ABA 021001088
HSBC Bank USA

For credit to:
Account: 000112046
Vanguard Incoming Wire Account

In favor of:
Vanguard Calvert Social Index Fund-.
[Account number, or temporary number for a new account]
[Registered account owner(s)]
[Registered address]
<PAGE>


                                                                              15

- --------------------------------------------------------------------------------
BY MAIL TO . . .[ENVELOPE]
open a new account
Complete and sign the account registration form and enclose your check.

add to an existing account
Mail your check with an Invest-By-Mail form detached from your confirmation
statement to the address listed on the form. Please do not alter Invest-By-Mail
forms, since they are fund- and account-specific.

Make your check payable to: The Vanguard Group-.
All purchases must be made in U.S. dollars, and checks must be drawn on U.S.
banks.



First-class mail to:               Express or Registered mail to:
The Vanguard Group                 The Vanguard Group
P.O. Box 2900                      100 Vanguard Boulevard
Valley Forge, PA 19482-2900        Malvern, PA 19355




- --------------------------------------------------------------------------------
IMPORTANT  NOTE:  To prevent  check fraud,  Vanguard will not accept checks made
payable to third parties.
- --------------------------------------------------------------------------------
BY TELEPHONE TO . . .[TELEPHONE]
open a new account
Call Vanguard  Tele-Account* 24 hours a day--or your assigned Service  Associate
during business  hours--to  exchange from another Vanguard fund account with the
same registration (name, address,  taxpayer  identification  number, and account
type). (Note that some restrictions apply to index fund accounts.)

add to an existing account
Call Vanguard  Tele-Account* 24 hours a day--or your assigned Service  Associate
during business  hours--to  exchange from another Vanguard fund account with the
same registration (name, address,  taxpayer  identification  number, and account
type). (Note that some restrictions apply to index fund accounts.)



Vanguard Tele-Account
1-800-662-6273

*You must obtain a Personal  Identification Number (PIN) through Tele-Account at
least seven days before you request your first exchange.
- --------------------------------------------------------------------------------
IMPORTANT  NOTE:  Once  you  have  initiated  a  telephone   transaction  and  a
confirmation  number has been assigned,  the transaction  cannot be revoked.  We
reserve the right to refuse any purchase request.
- --------------------------------------------------------------------------------
You can redeem  (that is, sell or  exchange)  shares  purchased  by check at any
time.  However,   while  your  redemption  request  will  be  processed  at  the
next-determined  net asset value after it is received,  your redemption proceeds
will not be available  until payment for your  purchase is collected,  which may
take up to ten calendar days.
- --------------------------------------------------------------------------------
A NOTE ON LARGE PURCHASES
It is important that you call Vanguard  before you invest a large dollar amount.
It is our responsibility to consider the interests of all Fund shareholders, and
so we  reserve  the right to refuse any  purchase  that may  disrupt  the Fund's
operation or performance.
- --------------------------------------------------------------------------------

<PAGE>


16

REDEEMING SHARES

This section describes how you can redeem--that is, sell or exchange--the Fund's
shares.

When Selling Shares:
- -    Vanguard sends the redemption proceeds to you or a designated third party.*
- -    You can sell all or part of your Fund shares at any time.

*May require a signature guarantee; see footnote on page 18.

When Exchanging Shares:
- -    The redemption proceeds are used to purchase shares of a different Vanguard
     fund.
- -    You must meet the receiving fund's minimum investment requirements.
- -    Vanguard reserves the right to revise or terminate the exchange  privilege,
     limit the amount of an exchange, or reject an exchange at any time, without
     notice.
- -    In  order  to  exchange  into  an  acount  with  a  different  registration
     (including a different name, address, or taxpayer  identification  number),
     you must include the guaranteed signatures of all current account owners on
     your written instructions.

In both  cases,  your  transaction  will be based on the Fund's  next-determined
share price, subject to any special rules discussed in this prospectus.
- --------------------------------------------------------------------------------
NOTE:  Once a redemption  is initiated  and a  confirmation  number  given,  the
transaction CANNOT be canceled.
- --------------------------------------------------------------------------------


HOW TO REQUEST A REDEMPTION
You can request a redemption  from your Fund account in any one of two ways:  by
telephone, or by mail.
     The Vanguard funds whose shares you cannot  exchange online or by telephone
are VANGUARD U.S.  STOCK INDEX FUNDS,  VANGUARD  BALANCED  INDEX FUND,  VANGUARD
INTERNATIONAL  STOCK INDEX FUNDS,  VANGUARD REIT INDEX FUND, and VANGUARD GROWTH
AND INCOME FUND. These funds do, however, permit telephone exchanges within IRAs
and some other retirement accounts.
- --------------------------------------------------------------------------------
TELEPHONE REQUESTS [TELEPHONE]
Call Vanguard  Tele-Account 24 hours a day--or your assigned  Service  Associate
during business  hours--to sell or exchange shares. You can exchange shares from
this Fund to open an account in another  Vanguard  fund or to add to an existing
Vanguard fund account with an identical registration.
- --------------------------------------------------------------------------------
SPECIAL  INFORMATION:  We will automatically  establish the telephone redemption
option for your  account,  unless you instruct us  otherwise  in writing.  While
telephone  redemption is easy and convenient,  this account  feature  involves a
risk of loss from  unauthorized or fraudulent  transactions.  Vanguard will take
reasonable  precautions  to protect your  account from fraud.  You should do the
same by keeping your account information  private and immediately  reviewing any
account  statements  that  we  send  to  you.  Make  sure  to  contact  Vanguard
immediately about any transaction you believe to be unauthorized.
- --------------------------------------------------------------------------------
We reserve the right to refuse a telephone redemption if the caller is unable to
provide:
- -    The ten-digit account number.
- -    The name and address exactly as registered on the account.
<PAGE>


                                                                              17

- -    The primary Social Security or employer identification number as registered
     on the account.
- -    The Personal  Identification  Number (PIN),  if applicable  (for  instance,
     Tele-Account).

     Please note that Vanguard will not be  responsible  for any account  losses
due to telephone  fraud, so long as we have taken reasonable steps to verify the
caller's identity.  If you wish to remove the telephone  redemption feature from
your account, please notify us in writing.
- --------------------------------------------------------------------------------
A NOTE ON UNUSUAL CIRCUMSTANCES
Vanguard  reserves the right to revise or  terminate  the  telephone  redemption
privilege at any time,  without notice.  In addition,  Vanguard can stop selling
shares or postpone  payment at times when the New York Stock  Exchange is closed
or under any emergency  circumstances  as determined by the U.S.  Securities and
Exchange Commission.  If you experience difficulty making a telephone redemption
during  periods  of  drastic  economic  or market  change,  you can send us your
request  by  regular or express  mail.  Follow  the  instructions  on selling or
exchanging shares by mail in this section.
- --------------------------------------------------------------------------------
MAIL REQUESTS [ENVELOPE]
Send a letter of instruction signed by all registered  account holders.  Include
the fund name and  account  number and (if you are  selling) a dollar  amount or
number  of shares  OR (if you are  exchanging)  the name of the fund you want to
exchange  into and a dollar  amount or number of  shares.  To  exchange  into an
account  with a different  registration  (including a different  name,  address,
taxpayer identification number, or account type), you must provide Vanguard with
written  instructions  that  include the  guaranteed  signatures  of all current
owners of the fund from which you wish to redeem.


First-class mail to:               Express or Registered mail to:

The Vanguard Group                 The Vanguard Group
P.O. Box 2900                      100 Vanguard Boulevard
Valley Forge, PA 19482-2900        Malvern, PA19355
- --------------------------------------------------------------------------------
A NOTE ON LARGE REDEMPTIONS
It is important that you call Vanguard  before you redeem a large dollar amount.
It is our responsibility to consider the interests of all fund shareholders, and
so we reserve the right to delay  delivery of your  redemption  proceeds--up  to
seven days--if the amount may disrupt the Fund's operation or performance.
     If you redeem more than  $250,000  worth of Fund  shares  within any 90-day
period,  the  Fund  reserves  the  right  to pay  part or all of the  redemption
proceeds above $250,000  in-kind,  i.e., in securities,  rather than in cash. If
payment is made in-kind,  you may incur  brokerage  commissions  if you elect to
sell the securities for cash.
- --------------------------------------------------------------------------------

OPTIONS FOR REDEMPTION PROCEEDS
You may receive your redemption  proceeds in one of two ways: check, or exchange
to another Vanguard fund.
- --------------------------------------------------------------------------------
CHECK REDEMPTIONS
Normally,  Vanguard  will  mail  your  check  within  two  business  days  of  a
redemption.
- --------------------------------------------------------------------------------
<PAGE>


18

- --------------------------------------------------------------------------------
EXCHANGE REDEMPTIONS
As described  above, an exchange  involves using the proceeds of your redemption
to purchase shares of another Vanguard fund.
- --------------------------------------------------------------------------------


FOR OUR MUTUAL PROTECTION
For your best interests and ours, Vanguard applies these additional requirements
to redemptions:

REQUEST IN "GOOD ORDER"
All redemption requests must be received by Vanguard in "good order." This means
that your request must include:
- -    The Fund name and account number.
- -    The amount of the transaction (in dollars or shares).
- -    Signatures  of all owners  exactly as  registered  on the account (for mail
     requests).
- -    Signature guarantees (if required).*
- -    Any supporting legal documentation that may be required.
- -    Any outstanding certificates representing shares to be redeemed.

*For instance,  a signature guarantee must be provided by all registered account
shareholders  when redemption  proceeds are to be sent to a different  person or
address. A signature  guarantee may be obtained from most commercial and savings
banks, credit unions, trust companies, or member firms of a U.S. stock exchange.

TRANSACTIONS ARE PROCESSED AT THE NEXT-DETERMINED SHARE PRICE AFTER VANGUARD HAS
RECEIVED ALL REQUIRED INFORMATION.
- --------------------------------------------------------------------------------
LIMITS ON ACCOUNT ACTIVITY
Because  excessive  account  transactions can disrupt the management of the Fund
and increase  the Fund's costs for all  shareholders,  Vanguard  limits  account
activity as follows:
- -    You may make no more than TWO  SUBSTANTIVE  "ROUND TRIPS"  THROUGH THE FUND
     during any 12-month period.
- -    Your round trips through the Fund must be at least 30 days apart.
- -    The Fund may refuse a share purchase at any time, for any reason.
- -    Vanguard may revoke an investor's telephone exchange privilege at any time,
     for any reason.

A "round trip" is a redemption  from the Fund  followed by a purchase  back into
the  Fund.  Also  a  "round  trip"  covers  transactions   accomplished  by  any
combination  of methods,  including  transactions  conducted by check,  wire, or
exchange to/from another Vanguard fund. "Substantive" means a dollar amount that
Vanguard  determines,  in  its  sole  discretion,  could  adversely  affect  the
management of the Fund.
- --------------------------------------------------------------------------------
ALL TRADES ARE FINAL
Vanguard  will not cancel any  transaction  request  (including  any purchase or
redemption)  that we believe to be authentic once the request has been initiated
and a confirmation number assigned.
- --------------------------------------------------------------------------------
UNCASHED CHECKS
Please cash your distribution or redemption  checks promptly.  Vanguard will not
pay interest on uncashed checks.
- --------------------------------------------------------------------------------

<PAGE>


                                                                              19

TRANSFERRING REGISTRATION

You can  transfer  the  registration  of your Fund  shares to  another  owner by
completing a transfer form and sending it to Vanguard.



First-class mail to:               Express or Registered mail to:
The Vanguard Group                 The Vanguard Group
P.O. Box 2900                      100 Vanguard Boulevard
Valley Forge, PA 19482-2900        Malvern, PA19355
- --------------------------------------------------------------------------------


FUND AND ACCOUNT UPDATES

STATEMENTS AND REPORTS
We will send you account and tax  statements to help you keep track of your Fund
account  throughout  the year as well as when you are preparing  your income tax
returns.
     In addition,  you will  receive  financial  reports  about the Fund twice a
year.  These   comprehensive   reports  include  an  assessment  of  the  Fund's
performance  (and a comparison  to its industry  benchmark),  an overview of the
financial  markets,  a  report  from  the  advisers,  and the  Fund's  financial
statements which include a listing of the Fund's holdings.
     To keep  the  Fund's  costs  as low as  possible  (so  that  you and  other
shareholders can keep more of the Fund's investment earnings), Vanguard attempts
to  eliminate  duplicate  mailings  to the same  address.  When two or more Fund
shareholders  have the same last name and address,  we send just one Fund report
to that address--instead of mailing separate reports to each shareholder. If you
want us to send separate reports,  you may notify our Institutional  Division at
1-800-809-8102.
- --------------------------------------------------------------------------------
CONFIRMATION STATEMENT
Sent each time you buy,  sell, or exchange  shares;  confirms the trade date and
the amount of your transaction.
- --------------------------------------------------------------------------------
PORTFOLIO SUMMARY [BOOKLET]
Mailed  quarterly for most  accounts;  shows the market value of your account at
the close of the statement period, as well as distributions,  purchases,  sales,
and exchanges for the current calendar year.
- --------------------------------------------------------------------------------
FUND FINANCIAL REPORTS
Mailed in October and April for this Fund.
- --------------------------------------------------------------------------------
TAX STATEMENTS
Generally  mailed in January;  report previous year's dividend and capital gains
distributions, and proceeds from the sale of shares.
- --------------------------------------------------------------------------------


MANDATORY CONVERSION TO INVESTOR SHARES

The Fund reserves the right to convert an investor's  Institutional  Shares into
Investor  Shares of the Fund if the investor's  account  balance falls below $10
million. Any such conversion will be preceded by written notice to the investor.
No transaction fee will be imposed on share-class conversions.
<PAGE>

GLOSSARY OF INVESTMENT TERMS


ACTIVE MANAGEMENT
An investment approach that seeks to exceed the average returns of the financial
markets.  Active  managers  rely on research,  market  forecasts,  and their own
judgment and experience in selecting securities to buy and sell.

CAPITAL GAINS DISTRIBUTION
Payment to mutual fund  shareholders of gains realized on securities that a fund
has sold at a profit, minus any realized losses.

CASH RESERVES
Cash deposits,  short-term  bank deposits,  and money market  instruments  which
include U.S.  Treasury bills,  bank  certificates  of deposit (CDs),  repurchase
agreements, commercial paper, and banker's acceptances.

COMMON STOCK
A security  representing  ownership  rights in a  corporation.  A stockholder is
entitled  to share in the  company's  profits,  some of which may be paid out as
dividends.

DIVIDEND INCOME
Payment to  shareholders  of income from  interest or  dividends  generated by a
fund's investments.

EXPENSE RATIO
The percentage of a fund's average net assets used to pay its expenses. The
expense ratio includes management fees, administrative fees, and any 12b-1
distribution fees.

INDEX
An unmanaged group of securities whose overall performance is used as a standard
to measure investment performance.

INVESTMENT ADVISER
An  organization  that  makes  the  day-to-day   decisions  regarding  a  fund's
investments.

MUTUAL FUND
An  investment  company  that pools the money of many people and invests it in a
variety of securities in an effort to achieve a specific objective over time.

NET ASSET VALUE (NAV)
The market value of a mutual fund's total assets, minus liabilities,  divided by
the  number of shares  outstanding.  The value of a single  share is called  its
share value or share price.

PASSIVE MANAGEMENT
A low-cost  investment strategy in which a mutual fund attempts to match--rather
than  outperform--a  particular  stock  or bond  market  index.  Also  known  as
indexing.

PRINCIPAL
The amount of your own money you put into an investment.

SECURITIES
Stocks, bonds, money market instruments, and other investment vehicles.

TOTAL RETURN
A percentage change,  over a specified time period, in a mutual fund's net asset
value,  with the ending net asset value adjusted to account for the reinvestment
of all distributions of dividends and capital gains.

VOLATILITY
The  fluctuations  in value of a mutual  fund or other  security.  The greater a
fund's volatility, the wider the fluctuations between its high and low prices.

YIELD
Income  (interest  or  dividends)  earned  by  an  investment,  expressed  as  a
percentage of the investment's price.
<PAGE>

[SHIP]
[THE VANGUARD GROUP LOGO]
Institutional Division
Post Office Box 2900
Valley Forge, PA 19482-2900

FOR MORE INFORMATION
If you'd like more information about
Vanguard Calvert Social Index Fund,
the following documents are
available free upon request:

ANNUAL/SEMIANNUAL REPORT TO SHAREHOLDERS
Additional information about the
Fund's investments is available in
the Fund'sannual and semiannual
reports to shareholders. Statement of
Additional Information (SAI)
The SAI provides more detailed
information about the Fund.

The current annual and semiannual
reports and the SAI are incorporated
by reference into (and are thus
legally a part of) this prospectus.

To receive a free copy of the latest
annual or semiannual report or the
SAI, or to request additional
information about the Fund or other
Vanguard funds, pleasecontact us
as follows:

If you are an Individual Investor:
THE VANGUARD GROUP
INVESTOR INFORMATION
DEPARTMENT
P.O. BOX 2900
VALLEY FORGE, PA
19482-2900

TELEPHONE: 1-800-662-7447 (SHIP)

TEXT TELEPHONE: 1-800-952-3335

If you are a client of Vanguard's
Institutional Division:
THE VANGUARD GROUP
INSTITUTIONAL
INVESTOR INFORMATION
P.O. BOX 2900
VALLEY FORGE, PA 19482-2900

TELEPHONE:
1-888-809-8102

WORLD WIDE WEB:
WWW.VANGUARD.COM

If you are a current Fund shareholder
and would like information about
your account, account transactions,
and/or account statements, please call:

CLIENT SERVICES DEPARTMENT
TELEPHONE:
1-800-662-2739 (CREW)

TEXT TELEPHONE:
1-800-749-7273

INFORMATION PROVIDED BY THE
SECURITIES AND EXCHANGE
COMMISSION (SEC)
You can review and copy
information about the Fund
(including the SAI) at the SEC's
Public Reference Room in
Washington, DC. To find out more
about this public service, call the
SEC at 1-800-SEC-0330. Reports and
other information about the Fund are
also available on the SEC's website
(www.sec.gov), or you can receive
copies of this information, for a fee,
by writing the Public Reference
Section, Securities and Exchange
Commission, Washington, DC 20549-0102.

Fund's Investment Company Act file
number: 811-1027

(C) 2000 The Vanguard Group, Inc.
All rights reserved.
Vanguard Marketing Corporation,
Distributor.

 .-04/28/2000
<PAGE>
The Vanguard U.S. Growth and Vanguard International Growth Prospectuses from PEA
# 76 are incorporated by reference.


<PAGE>


                                     PART B

                             VANGUARD(R) WORLD FUNDS
                                   (THE TRUST)

                       STATEMENT OF ADDITIONAL INFORMATION



                               DECEMBER 17, 1999;
                             REVISED APRIL 28, 2000

This Statement is not a prospectus  but should be read in  conjunction  with the
Trust's current  Prospectuses  (dated December 17, 1999, and April 28, 2000). To
obtain the  Prospectuses  or an additional  1999 Annual Report to  Shareholders,
which  contains  the  Funds'  Financial  Statements  as hereby  incorporated  by
reference, please call:



                 INVESTOR INFORMATION DEPARTMENT 1-800-662-7447


                               TABLE OF CONTENTS

                                                                 PAGE
DESCRIPTION OF THE TRUST.........................................B-1
INVESTMENT POLICIES..............................................B-3
YIELD AND TOTAL RETURN...........................................B-9
SHARE PRICE......................................................B-10
PURCHASE OF SHARES...............................................B-11
REDEMPTION OF SHARES.............................................B-12
FUNDAMENTAL INVESTMENT LIMITATIONS...............................B-12
MANAGEMENT OF THE FUNDS..........................................B-14
INVESTMENT ADVISORY SERVICES.....................................B-17
PORTFOLIO TRANSACTIONS...........................................B-20
FINANCIAL STATEMENTS.............................................B-21
COMPARATIVE INDEXES..............................................B-21

                            DESCRIPTION OF THE TRUST


ORGANIZATION

The Trust was organized as Ivest Fund, a Massachusetts corporation,  in 1959. It
became  a  Maryland  corporation  in 1973,  and was  reorganized  as a  Delaware
business trust in June 1998. Prior to its  reorganization as a Delaware business
trust, the Trust was known as Vanguard World Fund, Inc.



     The Trust has the ability to offer  additional  funds or classes of shares.
There is no limit on the number of full and fractional shares that each Fund may
issue. Vanguard Calvert Social Index Fund offers two classes of shares, Investor
Shares and Institutional  Shares.  Institutional Shares of the Fund are avaialbe
only to those  investing at least $10 million in the Fund.  The Trust  currently
offers the following funds:


                            Vanguard U.S. Growth Fund
                       Vanguard International Growth Fund
                       Vanguard Calvert Social Index Fund
               (individually, the Fund; collectively, the Funds)

     The Vanguard U.S.  Growth Fund and Vanguard  International  Growth Fund are
registered  with the United  States  Securities  and  Exchange  Commission  (the
Commission) under the Investment  Company Act of 1940 (the 1940 Act) as open-end
diversified management investment companies.


                                      B-1
<PAGE>



Vanguard  Calvert  Social Index Fund is  registered  with the  Commission  as an
open-end nondiversified management investment company.



SERVICE PROVIDERS


     CUSTODIAN.  State  Street  Bank and Trust  Company,  225  Franklin  Street,
Boston, Massachusetts 02110 (for Vanguard U.S. Growth Fund), The Chase Manhattan
Bank,  N.A., 4 Chase MetroTech  Center,  Brooklyn,  New York 11245 (for Vanguard
International  Growth  Fund),  and . (for Vanguard  Calvert  Social Index Fund),
serve as the  custodians.  The custodians are  responsible  for  maintaining the
Funds' assets and keeping all necessary accounts and records.


     INDEPENDENT ACCOUNTANTS.  PricewaterhouseCoopers LLP, 30 South 17th Street,
Philadelphia,  Pennsylvania 19103, serves as the Funds' independent accountants.
The accountants audit each Fund's financial statements and provide other related
services.

     TRANSFER  AND   DIVIDEND-PAYING   AGENT.  The  Funds'  transfer  agent  and
dividend-paying  agent is The Vanguard  Group,  Inc.,  100  Vanguard  Boulevard,
Malvern, Pennsylvania 19355.


CHARACTERISTICS OF THE FUNDS SHARES

     RESTRICTIONS  ON HOLDING OR DISPOSING OF SHARES.  There are no restrictions
on the right of  shareholders  to retain or dispose of the Funds' shares,  other
than the possible future  termination of the Funds.  Each Fund may be terminated
by reorganization into another mutual fund or by liquidation and distribution of
the assets of the  affected  series.  Unless  terminated  by  reorganization  or
liquidation, each Fund will continue indefinitely.

     SHAREHOLDER  LIABILITY.  The Funds are organized  under Delaware law, which
provides  that  shareholders  of a  business  trust  are  entitled  to the  same
limitations of personal  liability as  shareholders  of a corporation  organized
under  Delaware law.  Effectively,  this means that a shareholder of a Fund will
not be personally liable for payment of the Fund's debts except by reason of his
or her own conduct or acts. In addition,  a shareholder  could incur a financial
loss on account of a Fund  obligation  only if the Fund itself had no  remaining
assets with which to meet such  obligation.  We believe that the  possibility of
such a situation arising is extremely remote.


     DIVIDEND  RIGHTS.  The  shareholders  of a Fund are entitled to receive any
dividends or other distributions declared for such Fund. No shares have priority
or  preference  over  any  other  shares  of  the  same  Fund  with  respect  to
distributions. Distributions will be made from the assets of a Fund, and will be
paid ratably to all  shareholders of the Fund (or class) according to the number
of shares of such Fund (or class) held by  shareholders  on the record date. The
amount of income  dividends per share may vary between separate share classes of
the same Fund based upon  differences  in the way that  expenses  are  allocated
between share classes pursuant to a multiple class plan.

     VOTING  RIGHTS.  Shareholders  are  entitled  to vote on a matter if: (i) a
shareholder  vote is required  under the 1940 Act;  (ii) the matter  concerns an
amendment to the Declaration of Trust that would adversely  affect to a material
degree the rights  and  preferences  of the shares of any Fund or any class of a
Fund;  or (iii) the  Trustees  determine  that it is  necessary  or desirable to
obtain a  shareholder  vote.  The 1940 Act  requires  a  shareholder  vote under
various  circumstances,  including to elect or remove  Trustees upon the written
request of shareholders  representing 10% or more of a Fund's net assets, and to
change any fundamental  policy of a Fund.  Shareholders of each Fund receive one
vote for  each  dollar  of net  asset  value  owned on the  record  date,  and a
fractional  vote for each  fractional  dollar  of net asset  value  owned on the
record  date.  However,  only the shares of the Fund  affected  by a  particular
matter are entitled to vote on that matter. Voting rights are non-cumulative and
cannot be modified without a majority vote.



     LIQUIDATION  RIGHTS.  In the  event of  liquidation,  shareholders  will be
entitled to receive a pro rata share of the applicable Fund's net assets.

     PREEMPTIVE RIGHTS. There are no preemptive rights associated with shares of
each Fund.

                                      B-2
<PAGE>



     CONVERSION  RIGHTS.  Shareholders  of a Fund may convert  their shares into
another  class of  shares of the same  Fund  upon the  satisfaction  of any then
applicable eligibility requirements.


     REDEMPTION  PROVISIONS.  Each Fund's redemption provisions are described in
its  current   prospectuses  and  elsewhere  in  this  Statement  of  Additional
Information.

     SINKING FUND PROVISIONS. The Funds have no sinking fund provisions.

     CALLS OR ASSESSMENT.  Each Fund's shares,  when issued,  are fully paid and
non-assessable.


TAX STATUS OF THE FUNDS

Each  Fund  intends  to  qualify  as  a  "regulated  investment  company"  under
Subchapter M of the Internal  Revenue Code. This special tax status means that a
Fund will not be liable for federal tax on income and capital gains  distributed
to shareholders. In order to preserve its tax status, each Fund must comply with
certain requirements.  If a Fund fails to meet these requirements in any taxable
year, it will be subject to tax on its taxable  income at corporate  rates,  and
all distributions from earnings and profits,  including any distributions of net
tax-exempt   income  and  net  long-term  capital  gains,  will  be  taxable  to
shareholders  as ordinary  income.  In  addition,  the Fund could be required to
recognize  unrealized  gains,  pay  substantial  taxes  and  interest,  and make
substantial  distributions  before  regaining  its  tax  status  as a  regulated
investment company.


                              INVESTMENT POLICIES

The following policies  supplement each Fund's investment  policies set forth in
the Prospectus for each Fund.



     FUTURES  CONTRACTS  AND  OPTIONS.  Each Fund may enter into  stock  futures
contracts,  options, and options on futures contracts for the following reasons:
to maintain  cash  reserves  while  simulating  full  investment,  to facilitate
trading,  to reduce transaction costs, or to seek higher investment returns when
a futures  contract  is priced  more  attractively  than the  underlying  equity
security or index.  Vanguard Calvert Social Index Fund's  investments in futures
contracts  and  options  will not be screened  based on social or  environmental
criteria.  Futures  contracts  provide  for the  future  sale by one  party  and
purchase  by another  party of a  specified  amount of a specific  security at a
specified  future time and at a specified  price.  Futures  contracts  which are
standardized as to maturity date and underlying  financial instrument are traded
on national futures exchanges. Futures exchanges and trading are regulated under
the Commodity Exchange Act by the Commodity Futures Trading Commission (CFTC), a
U.S. Government Agency. Assets committed to futures contracts will be segregated
to the extent required by law.


     Although  futures  contracts  by their  terms call for actual  delivery  or
acceptance of the underlying securities,  in most cases the contracts are closed
out before the settlement date without the making or taking of delivery. Closing
out an open futures position is done by taking an opposite position  ("buying" a
contract  which has  previously  been  "sold,"  "selling" a contract  previously
purchased)  in an  identical  contract  to  terminate  the  position.  Brokerage
commissions are incurred when a futures contract is bought or sold.



     Futures traders are required to make a good faith initial margin deposit in
cash or  government  securities  with a broker  or  custodian  to  initiate  and
maintain open  positions in futures  contracts.  A margin deposit is intended to
assure  completion of the contract  (delivery or  acceptance  of the  underlying
security) if it is not terminated prior to the specified  delivery date. Minimal
initial margin  requirements  are established by the futures exchange and may be
changed.  Brokers may establish deposit  requirements  which are higher than the
exchange  minimums.  Futures  contracts  are  customarily  purchased and sold on
margin  that may range  upward  from  less than 5% of the value of the  contract
being traded.


     After a futures contract  position is opened,  the value of the contract is
marked to market daily. If the futures contract price changes to the extent that
the  margin  on  deposit  does  not  satisfy  margin  requirements,  payment  of
additional "variation" margin will be required. Conversely, change in the

                                      B-3
<PAGE>


contract  value may reduce the  required  margin,  resulting  in a repayment  of
excess margin to the contract holder.  Variation margin payments are made to and
from the futures  broker for as long as the  contract  remains  open.  Each Fund
expects to earn interest income on its margin deposits.

     Traders in futures contracts may be broadly  classified as either "hedgers"
or   "speculators."   Hedgers  use  the  futures  markets  primarily  to  offset
unfavorable  changes in the value of securities  otherwise  held for  investment
purposes or expected to be acquired by them.  Speculators  are less  inclined to
own the securities  underlying the futures  contracts which they trade,  and use
futures contracts with the expectation of realizing profits from fluctuations in
the market value of the underlying securities.  Each Fund intends to use futures
contracts only for bona fide hedging purposes.

     Regulations  of the CFTC  applicable  to each Fund  require that all of its
futures  transactions  constitute bona fide hedging  transactions  except to the
extent that the aggregate initial margins and premiums required to establish any
non-hedging  positions do not exceed five percent of the value of the respective
Fund's  portfolio.  Each  Fund  will  only sell  futures  contracts  to  protect
securities  it owns  against  price  declines or purchase  contracts  to protect
against an  increase  in the price of  securities  it intends  to  purchase.  As
evidence of this hedging interest,  each Fund expects that  approximately 75% of
its futures contract purchases will be "completed";  that is, equivalent amounts
of related  securities  will have been purchased or are being  purchased by each
Fund upon sale of open futures contracts.

     Although  techniques other than the sale and purchase of futures  contracts
could be used to control the exposure of a Fund's income to  fluctuations in the
market value of the underlying securities, the use of futures contracts may be a
more  effective  means of  hedging  this  exposure.  While the Funds  will incur
commission  expenses in both  opening and closing out futures  positions,  these
costs are lower than  transaction  costs  incurred in the  purchase  and sale of
portfolio securities.

     RESTRICTIONS ON THE USE OF FUTURES CONTRACTS. Each Fund will not enter into
futures contract transactions to the extent that,  immediately  thereafter,  the
sum of its initial margin  deposits on open  contracts  exceeds 5% of the Fund's
total assets.  In addition,  each Fund will not enter into futures  contracts to
the extent that its outstanding  obligations to purchase  securities under these
contracts would exceed 20% of the Fund's total assets.

     RISK FACTORS IN FUTURES TRANSACTIONS. Positions in futures contracts may be
closed  out only on an  exchange  which  provides  a  secondary  market for such
futures.  However, there can be no assurance that a liquid secondary market will
exist for any particular futures contract at any specific time. Thus, it may not
be  possible  to  close a  futures  position.  In the  event  of  adverse  price
movements,  each Fund would  continue to be required to make daily cash payments
to  maintain  its  required  margin.  In  such  situations,   if  the  Fund  has
insufficient cash, it may have to sell portfolio securities to meet daily margin
requirements  at a time when it may be  disadvantageous  to do so. In  addition,
each Fund may be required to make delivery of the instruments underlying futures
contracts it holds.  The inability to close options and futures  positions  also
could have an adverse impact on the ability to effectively hedge. Each Fund will
minimize the risk that it will be unable to close out a futures contract by only
entering into futures  contracts which are traded on national futures  exchanges
and for which there appears to be a liquid secondary market.

     The risk of loss in trading  futures  contracts in some  strategies  can be
substantial,  due both to the low margin  deposits  required,  and the extremely
high degree of leverage  involved in futures pricing.  As a result, a relatively
small  price  movement  in a  futures  contract  may  result  in  immediate  and
substantial loss (as well as gain) to the investor. For example, if, at the time
of purchase,  10% of the value of the futures contract is deposited as margin, a
subsequent  10% decrease in the value of the futures  contract would result in a
total  loss of the margin  deposit,  before any  deduction  for the  transaction
costs,  if the account  were then closed out. A 15%  decrease  would result in a
loss equal to 150% of the original  margin  deposit if the contract  were closed
out.  Thus,  a purchase  or sale of a futures  contract  may result in losses in
excess of the amount  invested  in the  contract.  However,  because the futures
strategies of each Fund are engaged in only for hedging purposes, the

                                      B-4
<PAGE>


investment  advisers do not  believe  that the Funds are subject to the risks of
loss frequently associated with futures transactions. Each Fund would presumably
have sustained  comparable  losses if, instead of the futures  contract,  it had
invested in the underlying financial instrument and sold it after the decline.

     Utilization  of futures  transactions  by a Fund does  involve  the risk of
imperfect or no correlation  where the securities  underlying  futures contracts
have different maturities than the portfolio securities being hedged. It is also
possible that a Fund could both lose money on futures contracts and experience a
decline in the value of its portfolio securities. There is also the risk of loss
by a Fund of margin  deposits in the event of  bankruptcy  of a broker with whom
the Fund has an open position in a futures contract or related option.

     Most futures exchanges limit the amount of fluctuation permitted in futures
contract  prices during a single  trading day. The daily limit  establishes  the
maximum  amount that the price of a futures  contract may vary either up or down
from the previous day's settlement  price at the end of a trading session.  Once
the daily limit has been reached in a particular type of contract, no trades may
be made on that day at a price beyond that limit.  The daily limit  governs only
price  movement  during a particular  trading day and  therefore  does not limit
potential  losses,  because the limit may prevent the liquidation of unfavorable
positions.  Futures contract prices have  occasionally  moved to the daily limit
for  several  consecutive  trading  days  with  little  or no  trading,  thereby
preventing  prompt  liquidation of future  positions and subjecting some futures
traders to substantial losses.

     FEDERAL TAX TREATMENT OF FUTURES  CONTRACTS.  Except for transactions  each
Fund has identified as hedging  transactions,  each Fund is required for federal
income  tax  purposes  to  recognize  as income  for each  taxable  year its net
unrealized gains and losses on futures  contracts held as of the end of the year
as well as those actually  realized during the year. In most cases,  any gain or
loss  recognized  with  respect to a futures  contract is  considered  to be 60%
long-term capital gain or loss and 40% short-term  capital gain or loss, without
regard to the  holding  period of the  contract.  (Different  rules may apply to
foreign futures  contracts.)  Furthermore,  sales of futures contracts which are
intended to hedge against a change in the value of securities  held by each Fund
may affect the holding period of such securities and,  consequently,  the nature
of the  gain or loss on such  securities  upon  disposition.  The  Funds  may be
required to defer the  recognition of losses on futures  contracts to the extent
of any unrecognized gains on related positions held by the Funds.

     In order for each Fund to  continue  to  qualify  for  federal  income  tax
treatment as a regulated  investment  company,  at least 90% of its gross income
for a taxable  year must be derived from  qualifying  income;  i.e.,  dividends,
interest,  income derived from loans of  securities,  and gains from the sale of
securities or foreign  currencies,  or other income  derived with respect to its
business  of  investing  in  such  stock,  securities,   or  currencies.  It  is
anticipated that any net gain realized from the closing out of futures contracts
will be considered qualifying income for purposes of the 90% requirement.

     Each Fund will  distribute to  shareholders  annually any net capital gains
which have been recognized for federal income tax purposes (including unrealized
gains at the end of the  Fund's  fiscal  year)  on  futures  transactions.  Such
distributions  will be combined with  distributions of capital gains realized on
the Fund's other  investments and shareholders  will be advised on the nature of
the payments.



     FOREIGN INVESTMENTS.  Vanguard International Growth Fund seeks to diversify
its assets among  various  foreign stock markets and, with respect to 65% of its
gross  assets,  will  invest  in the  securities  of at  least  three  different
countries.  Vanguard  U.S.  Growth  Fund may  invest up to 20% of its  assets in
securities of foreign  companies.  Vanguard Calvert Social Index Fund may invest
in  foreign  securities  to the  extent  necessary  to carry out its  investment
strategy  of holding  the stocks that  comprise  the index it tracks.  Investors
should  recognize that investing in foreign  companies  involves certain special
considerations  which  are  not  typically  associated  with  investing  in U.S.
companies.


                                      B-5
<PAGE>



     CURRENCY  RISK.  Since  the  stocks of  foreign  companies  are  frequently
denominated  in foreign  currencies,  and since the Funds may  temporarily  hold
uninvested  reserves in bank deposits in foreign  currencies,  the Funds will be
affected  favorably or  unfavorably by changes in currency rates and in exchange
control regulations,  and may incur costs in connection with conversions between
various  currencies.  The investment policies of Vanguard  International  Growth
Fund and  Vanguard  Calvert  Social  Index Fund permit it to enter into  forward
foreign  currency  exchange  contracts in order to hedge the Fund's holdings and
commitments  against  changes  in the  level  of  future  currency  rates.  Such
contracts  involve an  obligation  to purchase or sell a specific  currency at a
future date at a price set at the time of the contract.


     FEDERAL TAX  TREATMENT OF NON-U.S.  TRANSACTIONS.  Special rules govern the
Federal income tax treatment of certain  transactions  denominated in terms of a
currency  other than the U.S.  dollar or determined by reference to the value of
one or more  currencies  other than the U.S.  dollar.  The types of transactions
covered by the special rules include the following:  (i) the  acquisition of, or
becoming the obligor under, a bond or other debt instrument  (including,  to the
extent provided in Treasury regulations,  preferred stock); (ii) the accruing of
certain  trade  receivables  and  payables;  and  (iii)  the  entering  into  or
acquisition  of any  forward  contract,  futures  contract,  option  or  similar
financial instrument if such instrument is not marked to market. The disposition
of a currency other than the U.S. dollar by a U.S. taxpayer is also treated as a
transaction   subject  to  the  special   currency   rules.   However,   foreign
currency-related regulated futures contracts and nonequity options are generally
not  subject to the  special  currency  rules if they are or would be treated as
sold for their fair market value at year-end under the  marking-to-market  rules
applicable  to other futures  contracts  unless an election is made to have such
currency rules apply. With respect to transactions covered by the special rules,
foreign currency gain or loss is calculated  separately from any gain or loss on
the underlying  transaction and is normally  taxable as ordinary gain or loss. A
taxpayer  may elect to treat as capital gain or loss  foreign  currency  gain or
loss arising from certain identified  forward  contracts,  futures contracts and
options  that are capital  assets in the hands of the taxpayer and which are not
part of a straddle.  The  Treasury  Department  issued  regulations  under which
certain  transactions  subject to the special  currency rules that are part of a
"section 988 hedging  transaction"  (as defined in the Internal  Revenue Code of
1986, as amended,  and the Treasury  regulations) will be integrated and treated
as a single  transaction or otherwise  treated  consistently for purposes of the
Code.  Any gain or loss  attributable  to the foreign  currency  component  of a
transaction  engaged in by a Fund which is not subject to the  special  currency
rules (such as foreign equity  investments  other than certain preferred stocks)
will be treated as capital gain or loss and will not be segregated from the gain
or  loss on the  underlying  transaction.  It is  anticipated  that  some of the
non-U.S.  dollar-denominated  investments and foreign currency  contracts a Fund
may make or enter into will be subject to the special  currency rules  described
above.

     FOREIGN TAX CREDIT. Foreign governments may withhold taxes on dividends and
interest paid with respect to foreign  securities.  Foreign governments may also
impose taxes on other payments or gains with respect to foreign securities.  If,
at the close of its  fiscal  year,  more than 50% of a Fund's  total  assets are
invested in  securities of foreign  issuers,  the Fund may elect to pass through
foreign  taxes paid,  and  thereby  allow  shareholders  to take a tax credit or
deduction on their tax returns.  If  shareholders  meet certain  holding  period
requirements  with  respect  to Fund  shares,  an  offsetting  tax credit may be
available. If shareholders do not meet the holding period requirements, they may
still be entitled to a deduction for certain  foreign  taxes.  In either case, a
shareholder's  tax statement will show more taxable income or capital gains than
was  actually  distributed  by the Fund,  but will  also show the  amount of the
available offsetting credit or deduction.

     A  shareholder  that is a  nonresident  alien for U.S.  tax purposes may be
subject to adverse U.S. tax consequences.  For example, dividends and short-term
capital  gains  paid by the Fund  will  generally  be  subject  to U.S.  federal
withholding tax at a rate of 30% (or lower treaty rate if  applicable).  Foreign
investors  are  urged to  consult  their tax  advisers  regarding  the U.S.  tax
treatment of ownership of shares in the Fund.

                                      B-6
<PAGE>


  COUNTRY RISK.  As foreign companies are not generally subject to uniform
accounting, auditing and financial reporting standards and practices comparable
to those applicable to domestic companies, there may be less publicly available
information about certain foreign companies than about domestic companies.
Securities of some foreign companies are generally less liquid and more volatile
than securities of comparable domestic companies. There is generally less
government supervision and regulation of stock exchanges, brokers and listed
companies than in the U.S. In addition, with respect to certain foreign
countries, there is the possibility of expropriation or confiscatory taxation,
political or social instability, or diplomatic developments which could affect
U.S. investments in those countries.

     Although the Funds will endeavor to achieve most favorable  execution costs
in  their  portfolio  transactions,  fixed  commissions  on many  foreign  stock
exchanges are generally higher than negotiated commissions on U.S. exchanges. In
addition,  it is expected  that the expenses for custodian  arrangements  of the
Funds'  foreign  securities  will be somewhat  greater than the expenses for the
custodian arrangements for handling U.S. securities of equal value.

     Certain foreign  governments  levy  withholding  taxes against dividend and
interest  income.  Although  in some  countries  a  portion  of  these  taxes is
recoverable,  the non-recovered portion of foreign withholding taxes will reduce
the income  received from foreign  companies held by the Funds.  However,  these
foreign  withholding taxes are not expected to have a significant  impact on the
Funds,  since  each Fund seeks  long-term  capital  appreciation  and any income
should be considered incidental.

     TURNOVER  RATE.  While the  turnover  rate is not a  limiting  factor  when
management deems changes appropriate, it is anticipated that the annual turnover
rate for each Fund will not  normally  exceed  100%.  A rate of turnover of 100%
could occur,  for example,  if all of the securities held by a Fund are replaced
within a period of one year. The portfolio  turnover rate for each Fund for each
of the fiscal years presented is set forth under "Financial Highlights," in each
Fund's Prospectus.

     ILLIQUID  SECURITIES.  Each Fund may  invest up to 15% of its net assets in
illiquid securities.  Illiquid securities are securities that may not be sold or
disposed of in the ordinary  course of business  within seven  business  days at
approximately the value at which they are being carried on the Fund's books.

     Each Fund may invest in restricted, privately placed securities that, under
the  Commission's  rules,  may be sold only to qualified  institutional  buyers.
Because these securities can be resold only to qualified  institutional  buyers,
they may be considered illiquid securities--meaning that they could be difficult
for the Fund to convert to cash if needed.

     If a  substantial  market  develops for a restricted  security  held by the
Fund, it will be treated as a liquid security, in accordance with procedures and
guidelines  approved by the Fund's Board of Trustees.  This  generally  includes
securities  that are  unregistered  that can be sold to qualified  institutional
buyers in accordance  with Rule 144A under the  Securities Act of 1933 (the 1933
Act). While the Fund's investment adviser determines the liquidity of restricted
securities  on  a  daily  basis,   the  Board  oversees  and  retains   ultimate
responsibility for the adviser's decisions.  Several factors the Board considers
in  monitoring  these  decisions  include  the  valuation  of  a  security,  the
availability  of  qualified   institutional  buyers,  and  the  availability  of
information on the security's issuer.

     REPURCHASE  AGREEMENTS.  Each Fund along with other members of the Vanguard
Group may invest in repurchase  agreements  with  commercial  banks,  brokers or
dealers  either for defensive  purposes due to market  conditions or to generate
income from its excess cash  balances.  A  repurchase  agreement is an agreement
under which the Fund  acquires a  fixed-income  security  (generally  a security
issued by the U.S.  Government or an agency thereof, a banker's  acceptance or a
certificate  of deposit) from a commercial  bank,  broker or dealer,  subject to
resale to the  seller  at an agreed  upon  price  and date  (normally,  the next
business day). A repurchase agreement may be considered a loan collateralized by
securities. The resale price reflects an agreed upon interest rate effective for
the period the  instrument  is held by the Fund and is unrelated to the interest
rate on the

                                      B-7
<PAGE>


underlying  instrument.  In these  transactions,  the securities acquired by the
Fund  (including  accrued  interest  earned  thereon) must have a total value in
excess of the value of the repurchase agreement and are held by a custodian bank
until  repurchased.   In  addition,  the  Trust's  Board  of  Trustees  monitors
repurchase agreement  transactions  generally and has established guidelines and
standards for review by the investment  adviser of the  creditworthiness  of any
bank, broker or dealer party to a repurchase agreement.

     The use of repurchase  agreements  involves certain risks. For example,  if
the other party to the agreement  defaults on its  obligation to repurchase  the
underlying  security at a time when the value of the security has declined,  the
Fund may incur a loss upon  disposition  of the security.  If the other party to
the  agreement   becomes   insolvent  and  subject  to  \\^   \\liquidation   or
reorganization  under the  Bankruptcy  Code or other laws, a court may determine
that the underlying security is collateral for a loan by the Fund not within the
control of the Fund and therefore the realization by the Fund on such collateral
may be automatically  stayed.  Finally,  it is possible that the Fund may not be
able to substantiate  its interest in the underlying  security and may be deemed
an  unsecured  creditor  of the other party to the  agreement.  While the Fund's
management  acknowledges these risks, it is expected that they can be controlled
through careful monitoring procedures.

     LENDING OF  SECURITIES.  Each Fund may lend its  investment  securities  to
qualified institutional  investors (typically brokers,  dealers, banks, or other
financial  institutions)  who need to  borrow  securities  in order to  complete
certain transactions, such as covering short sales, avoiding failures to deliver
securities  or  completing  arbitrage  operations.  By  lending  its  investment
securities,  a Fund attempts to increase its net  investment  income through the
receipt of  interest  on the loan.  Any gain or loss in the market  price of the
securities  loaned that might occur during the term of the loan would be for the
account of the Fund.  The terms and the structure  and the  aggregate  amount of
such loans must be consistent  with the 1940 Act, and the Rules and  Regulations
or  interpretations  of the Commission  thereunder.  These  provisions limit the
amount of securities a Fund may lend to 33 1/3% of the Fund's total assets,  and
require  that (a) the  borrower  pledge and  maintain  with the Fund  collateral
consisting of cash,  an  irrevocable  letter of credit or  securities  issued or
guaranteed  by the United  States  Government  having at all times not less than
100%  of the  value  of the  securities  loaned,  (b) the  borrower  add to such
collateral whenever the price of the securities loaned rises (i.e., the borrower
"marks  to the  market"  on a daily  basis),  (c) the  loan be made  subject  to
termination  by the  Fund  at any  time,  and (d) the  Fund  receive  reasonable
interest on the loan (which may include the Fund's investing any cash collateral
in interest  bearing  short-term  investments),  any  distribution on the loaned
securities  and any increase in their market value.  Loan  arrangements  made by
each  Fund  will  comply  with all  other  applicable  regulatory  requirements,
including the rules of the New York Stock Exchange,  which presently require the
borrower, after notice, to redeliver the securities within the normal settlement
time of three business days. All relevant facts and circumstances, including the
creditworthiness  of the broker,  dealer or  institution,  will be considered in
making decisions with respect to the lending of securities, subject to review by
the Trust's Board of Trustees.

     At the  present  time,  the Staff of the  Commission  does not object if an
investment  company pays  reasonable  negotiated  fees in connection with loaned
securities,  so long as such  fees  are set  forth  in a  written  contract  and
approved by the investment company's Trustees.  In addition,  voting rights pass
with the loaned  securities,  but if a material  event will occur  affecting  an
investment on loan, the loan must be called and the securities voted.

     VANGUARD INTERFUND LENDING PROGRAM.  The Commission has issued an exemptive
order  permitting  the Funds to  participate  in  Vanguard's  interfund  lending
program.  This program  allows the Vanguard  funds to borrow money from and loan
money to each other for temporary or emergency purposes.  The program is subject
to a number of conditions,  including the requirement that no fund may borrow or
lend money through the program unless it receives a more favorable interest rate
than is available from a typical bank for a comparable transaction. In addition,
a fund may  participate  in the  program  only if and to the  extent  that  such
participation is consistent with the

                                      B-8
<PAGE>


fund's  investment  objective  and  other  investment  policies.  The  Boards of
Trustees of the Vanguard funds are  responsible  for ensuring that the interfund
lending program  operates in compliance with all conditions of the  Commission's
exemptive order.

     TEMPORARY INVESTMENTS. The Funds may take temporary defensive measures that
are  inconsistent  with  the  Funds'  normal   fundamental  or   non-fundamental
investment  policies and  strategies  in response to adverse  market,  economic,
political or other  conditions.  Such measures could include  investments in (a)
highly  liquid  short-term  fixed  income  securities  issued by or on behalf of
municipal or  corporate  issuers,  obligations  of the U.S.  Government  and its
agencies,  commercial  paper,  and bank  certificates of deposit;  (b) shares of
other  investment  companies  which have investment  objectives  consistent with
those of the Fund; (c) repurchase agreements involving any such securities;  and
(d) other money market instruments. There is no limit on the extent to which the
Funds may take temporary defensive measures. In taking such measures,  each Fund
may fail to achieve its investment objective.





                             YIELD AND TOTAL RETURN

The yield of Vanguard  U.S.  Growth Fund for the 30-day  period ended August 31,
1999, was 0.32%.

     The average  annual  total  return of each Fund for certain  periods  ended
August 31, 1999, is set forth below:


                                          1 YEAR      5 YEARS      10 YEARS
                                           ENDED        ENDED         ENDED
                                       8/31/1999     8/31/1999     8/31/1999
                                       ----------   -----------   -----------
Vanguard U.S. Growth Fund                +37.38%       +26.12%       +18.21%
Vanguard International Growth Fund       +21.70%        +9.85%        +8.98%
Vanguard Calvert Social Index Fund           N/A           N/A           N/A



AVERAGE ANNUAL TOTAL RETURN

Average annual total return is the average annual  compounded rate of return for
the  periods of one year,  five  years,  ten years or the life of the Fund,  all
ended on the last day of a recent month.  Average annual total return quotations
will  reflect  changes  in the price of the Fund's  shares  and assume  that all
dividends and capital gains  distributions  during the  respective  periods were
reinvested in Fund shares.  Average annual total return is calculated by finding
the average annual compounded rates of return of a hypothetical  investment over
such periods  according to the following formula (average annual total return is
then expressed as a percentage):

                               T = (ERV/P)1/N-1

  Where:

          T    =average annual total return
          P    =a hypothetical initial investment of $1,000
          n    =number of years
          ERV  =ending redeemable value: ERV is the value, at the end
               of the applicable period, of a hypothetical $1,000
               investment made at the beginning of the applicable
               period.

                                      B-9
<PAGE>


AVERAGE ANNUAL AFTER-TAX TOTAL RETURN QUOTATION

We calculate the Fund's  average  annual  after-tax  total return by finding the
average annual  compounded  rate of return over the 1-, 5-, and 10-year  periods
(or for periods of the Fund's  operations)  that would equate the initial amount
invested to the after-tax value, according to the following formulas:

After-tax return:

                                 P (1+T)N=ATV

  Where:

          P    =a hypothetical initial payment of $1,000
          T    =average annual after-tax total return
          n    =number of years
          ATV  =after-tax value at the end of the 1-,5-, or 10-year
               periods of a hypothetical $1,000 payment made at the
               beginning of the time period, assuming no liquidation
               of the investment at the end of the measurement
               periods.
Instructions:

1.   Assume all distributions by the Fund are  reinvested--less the taxes due on
     such  distributions--at  the price on the  reinvestment  dates  during  the
     period.  Adjustments  may be made for  subsequent  re-characterizations  of
     distributions.
2.   Calculate  the  taxes  due on  distributions  by the Fund by  applying  the
     highest federal  marginal tax rates to each component of the  distributions
     on the reinvestment date (e.g.,  ordinary income,  short-term capital gain,
     long-term  capital gain,  etc.).  For periods after  December 31, 1997, the
     federal marginal tax rates used for the calculations are 39.6% for ordinary
     income and  short-term  capital gains and 20% for long-term  capital gains.
     Note that the  applicable tax rates may vary over the  measurement  period.
     Assume no taxes are due on the portions of any distributions  classified as
     exempt  interest  or  non-taxable  (i.e.  return of  capital).  Ignore  any
     potential tax liabilities other than federal tax liabilities  (e.g.,  state
     and local taxes).
3.   Include all recurring  fees that are charged to all  shareholder  accounts.
     For any  account  fees that vary  with the size of the  account,  assume an
     account size equal to the Fund's mean (or median) account size. Assume that
     no  additional  taxes or tax credits  result from any  redemption of shares
     required to pay such fees.
4.   State the total return quotation to the nearest hundreth of one percent.

CUMULATIVE TOTAL RETURN

Cumulative  total  return is the  cumulative  rate of  return on a  hypothetical
initial  investment of $1,000 for a specified  period.  Cumulative  total return
quotations reflect changes in the price of the Fund's shares and assume that all
dividends and capital gains  distributions  during the period were reinvested in
Fund shares.  Cumulative  total return is calculated  by finding the  cumulative
rates of a return of a hypothetical  investment over such periods,  according to
the  following  formula   (cumulative  total  return  is  then  expressed  as  a
percentage):

                                 C = (ERV/P)-1

  Where:

          C    =cumulative total return
          P    =a hypothetical initial investment of $1,000
          ERV  =ending redeemable value: ERV is the value, at the end
               of the applicable period, of a hypothetical $1,000
               investment made at the beginning of the applicable
               period.

                                      B-10
<PAGE>


SEC YIELDS

Yield is the net  annualized  yield based on a  specified  30-day (or one month)
period  assuming  semiannual  compounding  of  income.  Yield is  calculated  by
dividing the net  investment  income per share  earned  during the period by the
maximum offering price per share on the last day of the period, according to the
following formula:

                          YIELD = 2[((A-B)/CD+1)6-1]

  Where:

          a    =dividends and interest earned during the period.
          b    =expenses accrued for the period (net of reimbursements).
          c    =the average daily number of shares outstanding during
               the period that were entitled to receive dividends.
          d    =the maximum offering price per share on the last day of
               the period.

                                  SHARE PRICE


Each Fund's  share  price,  or "net asset  value" per share,  is  calculated  by
dividing  the total  assets of each  Fund,  less all  liabilities,  by the total
number of shares outstanding. The net asset value for each share class of a Fund
is calculated by dividing the net assets attributable to each share class by the
total number of shares  outstanding for that share class. The net asset value is
determined  as of the  close  of the New  York  Stock  Exchange  (the  Exchange)
generally 4:00 p.m. Eastern time on each day the Exchange is open for trading.


     Portfolio  securities  for which market  quotations  are readily  available
(includes those securities listed on national securities  exchanges,  as well as
those quoted on the NASDAQ Stock Market) will be valued at the last quoted sales
price on the day the valuation is made. Such securities  which are not traded on
the  valuation  date are  valued  at the mean of the bid and ask  prices.  Price
information on  exchange-listed  securities is taken from the exchange where the
security is primarily  traded.  Securities  may be valued on the basis of prices
provided by a pricing  service when such prices are believed to reflect the fair
market value of such securities.

     Short-term instruments (those acquired with remaining maturities of 60 days
or less) may be valued at cost, plus or minus any amortized discount or premium,
which approximates market value.

     Bonds  and  other  fixed  income  securities  may be valued on the basis of
prices  provided by a pricing  service  when such prices are believed to reflect
the fair  market  value of such  securities.  The prices  provided  by a pricing
service  may be  determined  without  regard to bid or last sale  prices of each
security,  but take into  account  institutional-size  transactions  in  similar
groups of securities as well as any developments related to specific securities.

     Foreign  securities are valued at the last quoted sales price,  or the most
recently   determined  closing  price  calculated   according  to  local  market
convention, available at the time a Fund is valued. Prices are obtained from the
broadest and most representative market on which the securities trade. If events
which  materially  affect the value of each Fund's  investments  occur after the
close of the securities  markets on which such securities are primarily  traded,
those  investments  may be valued by such methods as the Board of Trustees deems
in good faith to reflect fair value.

     In  determining  each  Fund's  net asset  value per  share,  all assets and
liabilities  initially  expressed in foreign  currencies  will be converted into
U.S.  dollars using the  officially  quoted daily  exchange rates used by Morgan
Stanley Capital  International in calculating various benchmarking indices. This
officially quoted exchange rate may be determined prior to or after the close of
a particular  securities market. If such quotations are not available,  the rate
of exchange will be determined in accordance  with policies  established in good
faith by the Board of Trustees.

                                      B-11
<PAGE>


     Other assets and securities  for which no quotations are readily  available
or which are restricted as to sale (or resale) are valued by such methods as the
Board of Trustees deems in good faith to reflect fair value.

     The  share  price  for  each  Fund can be found  daily in the  mutual  fund
listings of most major newspapers under the heading of Vanguard Funds.



                               PURCHASE OF SHARES

The purchase  price of shares of each Fund is the net asset value per share next
determined  after  the  order is  received.  The net  asset  value  per share is
calculated  as of the  close  of the New  York  Stock  Exchange  on each day the
Exchange  is open for  business.  An order  received  prior to the  close of the
Exchange will be executed at the price  computed on the date of receipt;  and an
order  received  after the close of the  Exchange  will be executed at the price
computed on the next day the Exchange is open.



     Each Fund  reserves  the right in its sole  discretion  (i) to suspend  the
offering  of its  shares,  (ii) to impose a  transaction  fee on a purchase of a
Fund's  shares if the  purchase,  in the opinion of Vanguard,  would disrupt the
efficient  management of the Fund,  (iii) to reject  purchase orders when in the
judgment of management  such rejection is in the best interest of each Fund, and
(iv) to reduce or waive the minimum  investment for or any other restrictions on
initial and  subsequent  investments  for  certain  fiduciary  accounts  such as
employee  benefit plans or under  circumstances  where certain  economies can be
achieved in sales of a Fund's shares.

     EXCHANGE OF SECURITIES FOR SHARES OF VANGUARD CALVERT SOCIAL INDEX FUND. In
certain  circumstances,  shares of  Vanguard  Calvert  Social  Index Fund may be
purchased "in kind," i.e., in exchange for securities, rather than for cash. The
securities tendered as part of an in-kind purchase must be included in the Index
tracked by the Fund and must have a total market value of $1 million or more. In
addition,  each  position  must have a market  value of  $10,000  or more.  Such
securities  also  must be  liquid  securities  which  are not  restricted  as to
transfer  and have a value  that is  readily  ascertainable  as  evidenced  by a
listing on the American Stock  Exchange,  the New York Stock Exchange or NASDAQ.
Securities  accepted by the Fund will be valued as set forth under "Share Price"
in the Fund's  prospectus as of the time of the next  determination of net asset
value  after such  acceptance.  Shares of the Fund are issued at net asset value
determined as of the same time. All dividend, subscription, or other rights that
are  reflected  in the  market  price  of  accepted  securities  at the  time of
valuation  become the  property of the Fund and must be delivered to the Fund by
the investor upon receipt from the issuer. A gain or loss for Federal income tax
purposes would be realized by the investor upon the exchange  depending upon the
cost of the securities tendered.

     Vanguard  Calvert Social Index Fund will not accept  securities in exchange
for its shares  unless:  (1) such  securities  are, at the time of the exchange,
eligible to be held by the Fund; (2) the  transaction  will not cause the Fund's
weightings  to become  imbalanced  with respect to the  weightings of the stocks
included in the corresponding Index; (3) the investor represents and agrees that
all  securities  offered to the Fund are not  subject to any  restrictions  upon
their sale by the Fund under the Securities Act of 1933, or otherwise;  (4) such
securities are traded in an unrelated  transaction  with a quoted sales price on
the same day the exchange  valuation is made; (5) the quoted sales price used as
a basis of valuation is representative  (e.g., one that does not involve a trade
of substantial size that artificially influences the price of the security); and
(6) the value of any such  security  being  exchanged  will not exceed 5% of the
Fund's net assets immediately prior to the transaction.

     Investors  interested  in  purchasing  Fund shares with  securities  should
contact Vanguard.


TRADING SHARES THROUGH CHARLES SCHWAB

Each Fund has authorized  Charles  Schwab & Co., Inc.  (Schwab) to accept on its
behalf purchase and redemption orders under certain terms and conditions. Schwab
is also  authorized to designate  other  intermediaries  to accept  purchase and
redemption orders on each Fund's behalf subject to

                                      B-12
<PAGE>

those terms and conditions.  Under this arrangement,  the Fund will be deemed to
have  received a purchase or  redemption  order when  Schwab or, if  applicable,
Schwab's authorized  designee,  accepts the order in accordance with each Fund's
instructions.  Customer  orders that are  properly  transmitted  to each Fund by
Schwab,  or if  applicable,  Schwab's  authorized  designee,  will be  priced as
follows:

     Orders  received by Schwab before 3 p.m.  Eastern time on any business day,
will be sent to  Vanguard  that day and your  share  price  will be based on the
Fund's  net asset  value  calculated  at the close of trading  that day.  Orders
received by Schwab after 3 p.m.  Eastern  time,  will be sent to Vanguard on the
following  business  day and your  share  price  will be based on the Fund's net
asset value calculated at the close of trading that day.


                              REDEMPTION OF SHARES

The Funds may suspend redemption privileges or postpone the date of payment (i)
during any period that the New York Stock Exchange is closed, or trading on the
Exchange is restricted as determined by the Commission, (ii) during any period
when an emergency exists as defined by the rules of the Commission as a result
of which it is not reasonably practicable for a Fund to dispose of securities
owned by it, or fairly to determine the value of its assets, and (iii) for such
other periods as the Commission may permit.

     No charge is made by a Fund for  redemptions.  Shares redeemed may be worth
more or less than what was paid for them,  depending  on the market value of the
securities held by the Fund.

     If the Board of Trustees  determines  that it would be  detrimental  to the
best interests of the remaining shareholders of a Fund to make payment wholly or
partly  in cash,  a Fund may pay the  redemption  price in whole or in part by a
distribution in kind of readily  marketable  securities held by the Fund in lieu
of cash in conformity  with applicable  rules of the  Commission.  Investors may
incur brokerage charges on the sale of such securities so received in payment of
redemptions.

     SIGNATURE GUARANTEES.  To protect your account, the Funds and Vanguard from
fraud,  signature  guarantees  are required for certain  redemptions.  Signature
guarantees  enable  the  Funds  to  verify  the  identity  of a  person  who has
authorized a redemption from your account.  Signature guarantees are required in
connection  with: (1) all redemptions,  regardless of the amount involved,  when
the proceeds are to be paid to someone other than the registered  owner(s);  and
(2)  share  transfer   requests.   These  requirements  are  not  applicable  to
redemptions  in  Vanguard's  prototype  plans  except in  connection  with:  (1)
distributions  made when the proceeds  are to be paid to someone  other than the
plan participant;  (2) certain  authorizations to effect exchanges by telephone;
and (3) when proceeds are to be wired.  These  requirements may be waived by the
Funds in certain instances.

     Signature  guarantees  can be  obtained  from a bank,  broker  or any other
guarantor that Vanguard  deems  acceptable.  Notaries  public are not acceptable
guarantors.

     The signature guarantees must appear either: (1) on the written request for
redemption;  (2) on a separate  instrument  for  assignment  (stock power) which
should  specify the total number of shares to be  redeemed;  or (3) on all stock
certificates  tendered for  redemption  and, if shares held by the Fund are also
being redeemed, on the letter or stock power.

                       FUNDAMENTAL INVESTMENT LIMITATIONS

Each Fund is subject to the following fundamental investment limitations,  which
cannot be changed in any  material  way without the approval of the holders of a
majority of the affected  Fund's  shares.  For these  purposes,  a "majority" of
shares  means  shares  representing  the lesser of: (i) 67% or more of the votes
cast to  approve a change so long as  shares  representing  more than 50% of the
Fund's net asset value are present or  represented  by proxy;  or (ii) more than
50% of the Fund's net asset value.

                                      B-13
<PAGE>

     BORROWING.  Each  Fund  may not  borrow  money,  except  for  temporary  or
emergency purposes in an amount not exceeding 15% of the Fund's net assets. Each
Fund may borrow money through banks,  or Vanguard's  interfund  lending  program
only, and must comply with all applicable regulatory  conditions.  Each Fund may
not make any additional  investments whenever its outstanding  borrowings exceed
5% of net assets.


     COMMODITIES. Each Fund may not invest in commodities, except that each Fund
may invest in stock  futures  contracts,  stock  options,  and  options on stock
futures  contracts  and, in the case of Vanguard  International  Growth Fund and
Vanguard  Calvert  Social Index Fund,  foreign  currency  futures  contracts and
options.  No more than 5% of a Fund's total assets may be used as initial margin
deposit for futures contracts, and no more than 20% of a Fund's total assets may
be invested in futures contracts or options at any time.

     DIVERSIFICATION.  With respect to 75% of its total  assets,  Vanguard  U.S.
Growth Fund and Vanguard  International  Growth Fund may not: (i) purchase  more
than  10% of the  outstanding  voting  securities  of any  one  issuer,  or (ii)
purchase  securities  of any issuer if, as a result,  more than 5% of the Fund's
total assets would be invested in that issuer's securities. This limitation does
not apply to  obligations  of the United States  Government,  its  agencies,  or
instrumentalities.  Vanguard  Calvert Social Index Fund will limit the aggregate
value of all holdings  (except U.S.  Government and cash items, as defined under
subchapter M of the Internal  Revenue Code (the "Code")),  each of which exceeds
5% of  the  Fund's  total  assets,  to an  aggregate  of  50%  of  such  assets.
Additionally,  the Fund will limit the  aggregate  value of holdings of a single
issuer  (except  U.S.  Government  and cash items,  as defined in the Code) to a
maximum of 25% of the Fund's total assets.


     ILLIQUID  SECURITIES.  Each  Fund may not  acquire  any  security  if, as a
result, more than 15% of its net assets would be invested in securities that are
illiquid.

     INDUSTRY CONCENTRATION. Each Fund may not invest more than 25% of its total
assets in any one industry.

     INVESTING  FOR  CONTROL.  Each Fund may not  invest  in a  company  for the
purpose of controlling its management.

     INVESTMENT  COMPANIES.  Each Fund may not  invest  in any other  investment
company, except through a merger,  consolidation or acquisition of assets, or to
the extent permitted by Section 12 of the 1940 Act.  Investment  companies whose
shares the Fund acquires pursuant to Section 12 must have investment  objectives
and investment policies consistent with those of the Fund.

     LOANS.  Each Fund may not lend  money to any  person  except by  purchasing
fixed income  securities  that are publicly  distributed,  lending its portfolio
securities, or through Vanguard's interfund lending program

     MARGIN.  Each Fund may not purchase securities on margin or sell securities
short,  except as  permitted  by the  Funds'  investment  policies  relating  to
commodities.

     PLEDGING  ASSETS.  Each Fund may not pledge,  mortgage or hypothecate  more
than 15% of its net assets.

     REAL ESTATE. Each Fund may not invest directly in real estate,  although it
may invest in securities of companies that deal in real estate and bonds secured
by real estate.

     SENIOR  SECURITIES.  Each Fund may not issue senior  securities,  except in
compliance with the 1940 Act.

     UNDERWRITING.  Each Fund may not  engage in the  business  of  underwriting
securities  issued  by  other  persons.  The  Fund  will  not be  considered  an
underwriter when disposing of its investment securities.

     None of these  limitations  prevents  the Fund  from  participating  in The
Vanguard Group (Vanguard).  Because each Fund is a member of Vanguard, each Fund
may own securities issued by


                                      B-14
<PAGE>

Vanguard,  make loans to Vanguard,  and contribute to Vanguard's  costs or other
financial requirements. See "Management of the Funds" for more information.

     The  investment  limitations  set forth  above are  considered  at the time
investment securities are purchased.  If a percentage  restriction is adhered to
at the time the  investment is made, a later  increase in  percentage  resulting
from a change in the market  value of assets will not  constitute a violation of
such restriction.




                            MANAGEMENT OF THE FUNDS


OFFICERS AND TRUSTEES


The officers of the Funds manage its day-to-day  operations and are  responsible
to the Funds Board of Trustees.  The  Trustees set broad  policies for each Fund
and choose its officers. The following is a list of the Trustees and officers of
the Funds and a statement of their present  positions and principal  occupations
during the past five years. As a group, the Funds Trustees and officers own less
than 1% of the  outstanding  shares of each Fund.  Each Trustee also serves as a
Director of The Vanguard Group,  Inc., and as a Trustee of each of the 103 funds
administered  by Vanguard (102 in the case of Mr.  Malkiel and 93 in the case of
Mr. MacLaury).  The mailing address of the Trustees and officers of the Trust is
Post Office Box 876, Valley Forge, PA 19482.



JOHN J. BRENNAN, (DOB: 7/29/1954) Chairman, Chief Executive Officer &
Trustee*
Chairman,  Chief Executive Officer and Director of The Vanguard Group, Inc., and
Trustee of each of the investment companies in The Vanguard Group.

JOANN HEFFERNAN HEISEN, (DOB: 1/25/1950) Trustee
Vice President, Chief Information Officer, and member of the Executive Committee
of Johnson & Johnson (Pharmaceuticals/Consumer  Products), Director of Johnson &
Johnson*MERCK Consumer Pharmaceuticals Co., The Medical Center at Princeton, and
Women's Research and Education Institute.

BRUCE K. MACLAURY, (DOB: 5/7/1931) Trustee
President  Emeritus  of  The  Brookings  Institution  (Independent  Non-Partisan
Research  Organization);  Director of American  Express Bank, Ltd., The St. Paul
Companies, Inc. (Insurance and Financial Services), and National Steel Corp.

BURTON G. MALKIEL, (DOB: 8/28/1932) Trustee
Chemical Bank Chairman's Professor of Economics, Princeton University;  Director
of Prudential Insurance Co. of America, Banco Bilbao Gestinova, Baker Fentress &
Co.  (Investment  Management),  The Jeffrey Co.  (Holding  Company),  and Select
Sector SPDR Trust (Exchange-Traded Mutual Fund).

ALFRED M. RANKIN, JR., (DOB: 10/8/1941) Trustee
Chairman,  President,  Chief Executive Officer, and Director of NACCO Industries
(Machinery/Coal/  Appliances);  and  Director of The  BFGoodrich  Co.  (Aircraft
Systems/Manufacturing/Chemicals).

JOHN C. SAWHILL, (DOB: 6/12/1936) Trustee
President  and Chief  Executive  Officer of The Nature  Conservancy  (Non-Profit
Conservation Group);  Director of Pacific Gas and Electric Co., Procter & Gamble
Co., NACCO Industries (Machinery/Coal/ Appliances), and Newfield Exploration Co.
(Energy); formerly, Director and Senior Partner of McKinsey & Co., and President
of New York University.

JAMES O. WELCH, JR., (DOB: 5/13/1931) Trustee
Retired Chairman of Nabisco Brands, Inc. (Food Products);  retired Vice Chairman
and  Director  of RJR  Nabisco  (Food and  Tobacco  Products);  Director of TECO
Energy, Inc., and Kmart Corp.
                                      B-15
<PAGE>

J. LAWRENCE WILSON, (DOB: 3/2/1936) Trustee
Retired Chairman of Rohm & Haas Co. (Chemicals);  Director of Cummins Engine Co.
(Diesel Engine Company),  and The Mead Corp.  (Paper  Products);  and Trustee of
Vanderbilt University.

RAYMOND J. KLAPINSKY, (DOB: 12/7/1938) Secretary*
Managing Director of The Vanguard Group, Inc.;  Secretary of The Vanguard Group,
Inc. and of each of the investment companies in The Vanguard Group.

THOMAS J. HIGGINS, (DOB: 5/21/1957) Treasurer*
Principal  of The Vanguard  Group,  Inc.;  Treasurer  of each of the  investment
companies in The Vanguard Group.

ROBERT D. SNOWDEN, (DOB: 9/14/1961) Controller*
Principal of The Vanguard  Group,  Inc.;  Controller  of each of the  investment
companies in The Vanguard Group.

*Officers of the Trust are "interested persons" as defined in the Act.


THE VANGUARD GROUP

Each  Fund is a member  of The  Vanguard  Group of  Investment  Companies  which
consists of more than 100 funds.  Through their  jointly-owned  subsidiary,  The
Vanguard Group, Inc.  (Vanguard),  the Funds and the other funds in the Vanguard
Group obtain at-cost virtually all of their corporate management, administrative
and distribution  services.  Vanguard also provides investment advisory services
on an at-cost basis to several of the funds.

     Vanguard  employs  a  supporting  staff of  management  and  administrative
personnel needed to provide the requisite  services,  furnishings and equipment.
Each fund pays its share of Vanguard's  total expenses which are allocated among
the funds under  methods  approved  by the Board of  Trustees  of each fund.  In
addition,  each fund bears its own direct  expenses such as legal,  auditing and
custodian  fees.  In order to generate  additional  revenues  for  Vanguard  and
thereby   reduce  the  funds'   expenses,   Vanguard   also   provides   certain
administrative services to other organizations.

     Each fund's  officers  are also  officers and  employees  of  Vanguard.  No
officer or employee owns, or is permitted to own, any securities of any external
adviser for the funds.

  Vanguard adheres to a Code of Ethics established pursuant to Rule 17j-l under
the 1940 Act. The Code is designed to prevent unlawful practices in connection
with the purchase or sale of securities by persons associated with Vanguard.
Under Vanguard's Code of Ethics certain officers and employees of Vanguard who
are considered access persons are permitted to engage in personal securities
transactions. However, such transactions are subject to procedures and
guidelines similar to, and in many cases more restrictive than, those
recommended by a blue ribbon panel of mutual fund industry executives.

     Vanguard was  established and operates under an Amended and Restated Funds'
Service  Agreement which was approved by the  shareholders of each of the funds.
The amounts which each of the funds have invested are adjusted from time to time
in order to maintain the proportionate relationship between each fund's relative
net assets and its contribution to Vanguard's  capital. At August 31, 1999, each
fund had contributed  capital to Vanguard  representing 0.02% of each Fund's net
assets.  The  total  amount  contributed  by the  Funds  was  $5,111,000,  which
represented 5.1% of Vanguard's  capitalization.  The Amended and Restated Funds'
Service Agreement provides as follows: (a) each Vanguard fund may be called upon
to invest up to 0.40% of its  current  assets in  Vanguard,  and (b) there is no
other  limitation  on the dollar  amount each  Vanguard  fund may  contribute to
Vanguard's capitalization.

     MANAGEMENT.  Corporate management and administrative  services include: (1)
executive  staff;  (2) accounting and financial;  (3) legal and regulatory;  (4)
shareholder  account  maintenance;  (5)  monitoring  and  control  of  custodian
relationships;  (6)  shareholder  reporting;  and (7) review and  evaluation  of
advisory and other services provided to the Funds by third parties.

                                   B-16
<PAGE>


     DISTRIBUTION.  Vanguard Marketing Corporation, a wholly-owned subsidiary of
The Vanguard Group, Inc., provides all distribution and marketing activities for
the funds in the Group. The principal distribution expenses are for advertising,
promotional materials,  and marketing personnel.  Distribution services may also
include  organizing  and offering to the public,  from time to time, one or more
new investment  companies which will become members of The Vanguard  Group.  The
Trustees and officers of Vanguard  determine the amount to be spent  annually on
distribution  activities,  the manner  and amount to be spent on each fund,  and
whether to organize new investment companies.

     One half of the distribution expenses of a marketing and promotional nature
is allocated  among the funds based upon relative net assets.  The remaining one
half of those expenses is allocated among the funds based upon each fund's sales
for the preceding 24 months relative to the total sales of the funds as a Group,
provided,  however,  that no fund's aggregate quarterly rate of contribution for
distribution expenses of a marketing and promotional nature shall exceed 125% of
the average  distribution  expense rate for The Vanguard Group, and that no fund
shall  incur  annual  distribution  expenses  in excess of of 1% of its  average
month-end net assets.

     During  the last three  fiscal  years,  the Funds  incurred  the  following
approximate  amounts of The  Vanguard  Group's  management  (including  transfer
agency), distribution, and marketing expenses.


<TABLE>
<CAPTION>
- ----------------------------------------------------------------------------------------------------------
<S>                                                 <C>                 <C>                 <C>
FUND                                             FISCAL YEAR ENDED   FISCAL YEAR ENDED   FISCAL YEAR ENDED
                                                      8/31/1997           8/31/ 1998           8/31/1999
- ----------------------------------------------------------------------------------------------------------
U.S. Growth Fund                                     $16,574,000         $24,303,000         $36,880,000
International Growth Fund                             19,620,000          25,651,000          29,133,000
Calvert Social Index Fund                                    N/A                 N/A                 N/A
- ----------------------------------------------------------------------------------------------------------
</TABLE>




     INVESTMENT   ADVISORY  SERVICES.   Vanguard  provides  investment  advisory
services to Vanguard Calvert Social Index Fund and several other Vanguard funds.
These  services are provided on an at-cost basis from a money  management  staff
employed directly by Vanguard. The compensation and other expenses of this staff
are paid by the funds utilizing these services.



TRUSTEE COMPENSATION

The  same  individuals  serve  as  Trustees  of all  Vanguard  funds  (with  two
exceptions,  which are noted in the table appearing on page B-17), and each fund
pays a proportionate share of the Trustees' compensation. The funds employ their
officers on a shared basis,  as well.  However,  officers are compensated by The
Vanguard Group, Inc., not the funds.


     INDEPENDENT TRUSTEES. The funds compensate their independent Trustees--that
is, the ones who are not also officers of the funds--in three ways:

 . The independent Trustees receive an annual fee for their service to the funds,
  which is subject to reduction based on absences from scheduled Board meetings.

 . The independent Trustees are reimbursed for the travel and other expenses that
  they incur in attending Board meetings.

 . Upon retirement, the independent Trustees receive an aggregate annual fee of
  $1,000 for each year served on the Board, up to fifteen years of service. This
  annual fee is paid for ten years following retirement, or until each Trustee's
  death.


     "INTERESTED"  TRUSTEES. The funds' interested  Trustees--Messrs.  Bogle and
Brennan--receive  no compensation  for their service in that capacity.  However,
they are paid in their role as officers of The Vanguard Group, Inc.

     COMPENSATION TABLE. The following table provides  compensation  details for
each of the Trustees.  We list the amounts paid as  compensation  and accrued as
retirement benefits by each Fund for each Trustee. In addition,  the table shows
the total  amount of benefits  that we expect each  Trustee to receive  from all
Vanguard funds upon retirement, and the total amount of compensation


                               B-17
<PAGE>

paid to each Trustee by all Vanguard  funds.  All  information  shown is for the
fiscal year ended August 31, 1999.





<TABLE>
<CAPTION>
                                        TRUSTEES COMPENSATION TABLE
<S>                                              <C>             <C>            <C>                 <C>
                                                              PENSION OR
                                                              RETIREMENT                            TOTAL
                                                               BENEFITS                         COMPENSATION
                                                AGGREGATE      ACCRUED AS       ESTIMATED          FROM ALL
                                              COMPENSATION   PART OF THESE       ANNUAL            VANGUARD
                                               FROM THESE        FUNDS'       BENEFITS UPON    FUNDS PAID TO
 NAMES OF TRUSTEES                               FUNDS(1)      EXPENSES(1)      RETIREMENT       TRUSTEES(2)
- ---------------------------------------------------------------------------------------------------------------
John C. Bogle (3). . . .                          None            None             None              None
John J. Brennan . . .                             None            None             None              None
Barbara Barnes Hauptfuhrer(4). . .                $1,477          $187           $15,000                $0
JoAnn Heffernan Heisen                            $4,430          $244           $15,000           $80,000
Bruce K. MacLaury . .                             $4,590          $413           $12,000           $75,000
Burton G. Malkiel . .                             $4,462          $404           $15,000           $80,000
Alfred M. Rankin, Jr.                             $4,430          $295           $15,000           $80,000
John C. Sawhill . . .                             $4,430          $374           $15,000           $80,000
James O. Welch, Jr. .                             $4,430          $432           $15,000           $80,000
J. Lawrence Wilson. .                             $4,430          $312           $15,000           $80,000
</TABLE>


(1)  The amounts  shown in this column are based on the Funds' fiscal year ended
     October 31, 1999.
(2)  The amounts reported in this column reflect the total  compensation paid to
     each Trustee for his or her service as Trustee of 103  Vanguard  funds (102
     in the case of Mr.  Malkiel;  93 in the case of Mr.  MacLaury) for the 1999
     calendar year.
(3)  Mr. Bogle has retired from the Funds' Board, effective December 31, 1999.
(4)  Mrs. Hauptfuhrer has retired from the Funds' Board,  effective December 31,
     1998.



                          INVESTMENT ADVISORY SERVICES


VANGUARD U.S. GROWTH FUND INVESTMENT ADVISORY AGREEMENT

The Fund entered into an  investment  advisory  agreement  with Lincoln  Capital
Management  Company  (Lincoln),  under which Lincoln  manages the investment and
reinvestment   of  the  assets   included  in  Vanguard  U.S.  Growth  Fund  and
continuously  reviews,  supervises and administers the Fund. Lincoln will invest
or reinvest such assets  primarily in U.S.  securities.  Lincoln  discharges its
responsibilities  subject to the  control of the  officers  and  Trustees of the
Fund.  Under this  agreement the Fund pays Lincoln an advisory fee at the end of
each fiscal  quarter,  calculated  by applying a  quarterly  rate,  based on the
following annual  percentage  rates, to the Fund's average  month-end net assets
for the quarter:

          NET ASSETS                                  RATE
          ----------                                  ----
          First $25 million...............            .40%
          Next $125 million...............            .35%
          Next $350 million...............            .25%
          Next $500 million...............            .20%
          Next $1.5 billion...............            .15%
          Next $12.5 billion..............            .10%
          Over $15 billion................            .08%

                                      B-18
<PAGE>


     For the fiscal  years  ended  August 31,  1997,  1998,  and 1999,  the Fund
incurred advisory fees of $8,475,000, $11,377,000, and $16,307,000 respectively.


DESCRIPTION OF LINCOLN

Lincoln is an Illinois  corporation  in which a controlling  interest is held by
the following  persons:  Timothy H. Ubben,  Chairman;  J. Parker Hall III, Chief
Executive Officer;  Kenneth R. Meyer,  President;  Ray B. Zemon,  Executive Vice
President; David M. Fowler, Executive Vice President; Richard W. Knee, Executive
Vice President; and Jay H. Freedman, Executive Vice President.

     The agreement  with Lincoln is renewable for successive  one-year  periods,
only if each renewal is  specifically  approved by a vote of the Fund's Board of
Trustees,  including the affirmative votes of a majority of the Trustees who are
not parties to the  agreement  or  "interested  persons" (as defined in the 1940
Act) of any such  party,  cast in person at a meeting  called for the purpose of
considering  such  approval.  The  agreement  is  automatically   terminated  if
assigned,  and may be terminated  without penalty at any time (1) by vote of the
Board of Trustees of the Fund on sixty (60) days' written notice to Lincoln,  or
(2) by Lincoln upon ninety (90) days' written notice to the Fund.

     The  Trustees  may  make any of  these  changes  without  the  approval  of
shareholders,  however,  any such change will be communicated to shareholders in
writing.

VANGUARD INTERNATIONAL GROWTH FUND INVESTMENT ADVISORY AGREEMENT

Vanguard  International  Growth Fund has  entered  into an  investment  advisory
agreement with Schroder Investment  Management North America, Inc. (Schroder) to
manage the  investment  and  reinvestment  of Fund's assets and to  continuously
review,   supervise,   and  administer  Vanguard   International  Growth  Fund's
investment program. In this regard, it is the responsibility of Schroder to make
decisions  relating to the Fund's investment in foreign  securities and to place
the Fund's purchase and sale orders for such securities. Schroder will invest or
reinvest the assets of the Fund only in foreign (non-U.S.) securities.  Schroder
discharges  its  responsibilities  subject to the  control of the  officers  and
Trustees of the Trust.

     As compensation for the services  rendered by Schroder under the agreement,
the Fund pays Schroder a basic fee at the end of each fiscal quarter  calculated
by applying a quarterly rate, based on the following annual percentage rates, to
the average month-end net assets of the Fund for the quarter:


          NET ASSETS                                         RATE
          ----------                                         ----
          First $50 million...............                   .350%
          Next $950 million...............                   .175%
          Over $1 billion.................                   .125%


     The Basic Fee,  as provided  above,  shall be  increased  or  decreased  by
applying an adjustment  formula based on the investment  performance of Vanguard
International  Growth  Fund  relative  to that  of the  Morgan  Stanley  Capital
International Europe, Australasia, Far East (MSCI EAFE) Index as follows:


  (a)  On assets of the Fund of $1 billion or less:

            THREE-YEAR PERFROMANCE
             DIFFERENTIAL VS. MSCI                      ANNUAL INCENTIVE (+)/
                  EAFE INDEX                             PENALTY (-) FEE RATE
- --------------------------------------------------------------------------------

                                      B-19
<PAGE>

                +12% or above                                 +0.0750%
             Between +6% and +12%                             +0.0375%
              Between +6% and -6%                                -0-
             Between -6% and -12%                             -0.0375%
                -12% and below                                -0.0750%


  (b)  On assets of the Fund of more than $1 billion:

             THREE-YEAR PERFROMANCE
              DIFFERENTIAL VS. MSCI                       ANNUAL INCENTIVE (+)/
                   EAFE INDEX                              PENALTY (-) FEE RATE
- --------------------------------------------------------------------------------
                  +12% or above                                  +0.0500%
              Between +6% and +12%                               +0.0250%
               Between +6% and -6%                                 -0-
              Between -6% and -12%                               -0.0250%
                 -12% and below                                  -0.0500%



     The incentive/penalty fee adjustment for assets in excess of $1 billion was
not fully operable  until the quarter ended  February 29, 1996,  and, until that
date, was calculated  according to certain  transition rules. From April 1, 1993
through November 30, 1993, the  incentive/penalty  fee on assets in excess of $1
billion  was  not  operable.   For  quarters  ending  after  this  period,   the
incentive/penalty  fee  adjustment  on assets in excess of $1  billion  has been
computed  based on a comparison of the  investment  performance  of the Fund and
that of the MSCI EAFE Index over the number of months that have elapsed  between
March 1, 1993 and the end of the quarter for which the fee is computed.

     For  the  purpose  of   determining   the  fee  adjustment  for  investment
performance, as described above, the net assets of Vanguard International Growth
Fund are averaged over the same period as the investment performance of the Fund
and the investment record of the MSCI EAFE Index are computed.

     The investment  performance of Vanguard  International Growth Fund for such
period,  expressed as a percentage  of the net asset value per share of the Fund
at the beginning of such period,  shall be the sum of: (i) the change in the net
asset value per share of the Fund during such period; (ii) the value of the cash
distributions  per share of the Fund accumulated to the end of such period;  and
(iii) the value of capital  gains taxes per share paid or payable by the Fund on
undistributed  realized  long-term  capital gains accumulated to the end of such
period.  For this  purpose,  the value of  distributions  per share of  realized
capital gains, of dividends per share paid from investment income and of capital
gains  taxes per share  paid or  payable  on  undistributed  realized  long-term
capital  gains shall be treated as  reinvested  in shares of the Fund at the net
asset  value per share in effect at the close of business on the record date for
the payment of such  distributions and dividends and the date on which provision
is made for such taxes, after giving effect to such distributions, dividends and
taxes. The investment record of the MSCI EAFE Index for any period, expressed as
a percentage of the MSCI EAFE Index level at the beginning of such period, shall
be the sum of (i) the  change in the level of the MSCI EAFE  Index  during  such
period and (ii) the value,  computed  consistently  with the MSCI EAFE Index, of
cash  distributions  made by companies whose  securities  comprise the MSCI EAFE
Index accumulated to the end of such period. For this purpose cash distributions
on the  securities  which  comprise  the MSCI EAFE  Index  shall be  treated  as
reinvested  in the MSCI  EAFE  Index at least as  frequently  as the end of each
calendar  quarter   following  the  payment  of  the  dividend.   The  foregoing
notwithstanding,  any computation of the investment  performance of the Fund and
the  investment  record of the MSCI EAFE Index shall be in  accordance  with any
then applicable rules of the Commission.

  The Trustees believe that the MSCI EAFE Index is an appropriate standard
against which the investment performance of Vanguard International Growth Fund
can be measured. The MSCI EAFE

                                      B-20
<PAGE>

Index is the only index available which covers the major  international  markets
outside  North  America.  The  weighting of securities in the MSCI EAFE Index is
based on each stock's relative total market value, that is, its market price per
share times the number of shares outstanding.


     The agreement with Schroder is renewable for successive  one-year  periods,
only if each renewal is  specifically  approved by a vote of the Fund's Board of
Trustees,  including the affirmative votes of a majority of the Trustees who are
not parties to the  agreement  or  "interested  persons" (as defined in the 1940
Act) of any such  party,  cast in person at a meeting  called for the purpose of
considering  such  approval.  The  agreement  is  automatically   terminated  if
assigned,  and may be terminated  without penalty at any time (1) by vote of the
Board of Trustees of the Fund on sixty (60) days' written notice to Schroder, or
(2) by Schroder upon ninety (90) days' written notice to the Fund.


     During the three  fiscal  years ending  August 31,  1997,  1998,  and 1999,
respectively, the Fund paid Schroder the following advisory fees:


                                              1997         1998         1999
                                              ----         ----         ----
Basic Fee                               $8,245,000   $9,793,000  $10,068,000
Increase/(Decrease) for Performance
Adjustment                               1,980,000    2,526,000      418,000
Total                                  $10,225,000  $12,319,000  $10,486,000
                                       ===========  ===========  ===========

DESCRIPTION OF SCHRODER CAPITAL

Vanguard  International  Growth Fund is managed by the London  branch  office of
Schroder  Investment  Management  North  America,  Inc.  (SIMNA).   SIMNA  is  a
wholly-owned subsidiary of Schroders Incorporated, 787 7th Avenue, New York, New
York. Schroders PLC is the holding company parent of a large world-wide group of
banks and financial service companies (referred to as "The Schroder Group") with
associated companies and branch and representative  offices located in seventeen
countries.  The Schroder Group  specializes in providing  investment  management
services, with Group funds under management currently in excess of $200 billion.


     Vanguard  Calvert  Social  Index  Fund  receives   advisory  services  from
Vanguard's Core Management Group on an at-cost basis.




                             PORTFOLIO TRANSACTIONS

The  investment  advisory  agreements  with Lincoln and Schroder  authorize  the
investment  advisers  (with the  approval of the Funds'  Board of  Trustees)  to
select the  brokers or dealers  that will  execute  the  purchases  and sales of
portfolio securities for the Trust and direct each investment adviser to use its
best efforts to obtain the best  available  price and most  favorable  execution
with respect to all  transactions  for each Fund.  Each  investment  adviser has
undertaken  to execute each  investment  transaction  at a price and  commission
which provides the most favorable total cost or proceeds  reasonably  obtainable
under the circumstances.

     In placing  portfolio  transactions,  each investment  adviser will use its
best  judgment  to choose the broker most  capable of  providing  the  brokerage
services necessary to obtain best available price and most favorable  execution.
The full range and quality of brokerage services available will be considered in
making  these  determinations.   In  those  instances  where  it  is  reasonably
determined that more than one broker can offer the brokerage  services needed to
obtain the best available price and most favorable execution,  consideration may
be  given  to  those  brokers  which  supply  investment  research,  statistical
information,  or provide other services in addition to execution services to the
Funds and/or the investment  advisers.  Each  investment  adviser  considers
                                      B-21
<PAGE>

the investment services it receives useful in the performance of its obligations
under the agreement but is unable to determine the amount by which such services
may reduce its expenses.

     Currently,  it is each Fund's  policy that each  investment  adviser may at
times pay higher commissions in recognition of brokerage services felt necessary
for the achievement of better execution of certain securities  transactions than
otherwise  might not be  available.  An  investment  adviser  will only pay such
higher  commissions  if it believes  this to be in the best  interest of a Fund.
Some brokers or dealers who may receive such higher  commissions  in recognition
of brokerage  services related to execution of securities  transactions are also
providers of research  information to the investment  advisers and/or the Funds.
However,  each investment  adviser has informed the Funds that it generally will
not pay higher  commission  rates  specifically  for the  purpose  of  obtaining
research services.


     During the fiscal years ending August 31, 1997,  1998,  and 1999, the Funds
paid the following amounts in brokerage commissions:



          FUND                            1997         1998         1999
          ---                             ----         ----         ----
U.S. Growth Fund                       $4,076,812   $6,538,324  $11,950,441
International Growth Fund              $7,912,581  $10,369,101  $10,770,933
Calvert Social Index Fund                  N/A          N/A          N/A


     Some  securities  considered  for  investment  by the  Funds  may  also  be
appropriate  for  other  Vanguard  funds or  clients  served  by the  investment
advisers.  If  purchase or sale of  securities  consistent  with the  investment
policies of the Funds and one or more of these other funds or clients  served by
the investment  advisers are considered at or about the same time,  transactions
in such  securities  will be allocated among the Funds and the several funds and
clients in a manner  deemed  equitable  by the  respective  investment  adviser.
Although there will be no specified  formula for allocating  such  transactions,
the  allocation  methods  used,  and the  results of such  allocations,  will be
subject to periodic review by the Fund's Board of Trustees.


                              FINANCIAL STATEMENTS

The Financial Statements of Vanguard U.S. Growth Fund and Vanguard International
Growth  Fund as of and  for the  year  ended  August  31,  1999,  including  the
financial  highlights  for each of the five years in the period ended August 31,
1999,  appearing in the Funds'  respective 1999 Annual Reports to  Shareholders,
and the reports thereon of PricewaterhouseCoopers  LLP, independent accountants,
also  appearing  therein,  are  incorporated  by reference in this  Statement of
Additional  Information.  For a more  complete  discussion  of the  performance,
please see the Funds'  Annual  Reports to  Shareholders,  which may be  obtained
without charge.


                              COMPARATIVE INDEXES

Vanguard may use reprinted  material  discussing The Vanguard Group, Inc. or any
of the member funds of The Vanguard Group of Investment Companies.

     Each of the investment  company  members of The Vanguard  Group,  including
Vanguard  World Fund,  may from time to time,  use one or more of the  following
unmanaged indexes for comparative performance purposes.

STANDARD & POOR'S 500 COMPOSITE STOCK PRICE  INDEX--includes  stocks selected by
Standard & Poor's Index Committee to include  leading  industries and to reflect
the U.S. stock market.

STANDARD & POOR'S  MIDCAP 400  INDEX--is  composed of 400 medium sized  domestic
stocks.

STANDARD & POOR'S SMALL CAP 600/BARRA  VALUE  INDEX--contains  stocks of the S&P
SmallCap 600 Index which have a lower than average price-to-book ratio.

                                      B-22

<PAGE>

STANDARD & POOR'S SMALL CAP 600/BARRA GROWTH INDEX--contains stocks of the S&P
SmallCap 600 Index which have a higher than average price-to-book ratio.

RUSSELL 1000 VALUE INDEX--consists of the stocks in the Russell 1000 Index
(comprising the 1,000 largest U.S.-based companies measured by total market
capitalization) with the lowest price-to-book ratios, comprising 50% of the
market capitalization of the Russell 1000.

WILSHIRE  5000  EQUITY   INDEX--consists   of  more  than  7,000  common  equity
securities,  covering  all  stocks  in the  U.S.  for  which  daily  pricing  is
available.

WILSHIRE 4500 EQUITY  INDEX--consists  of all stocks in the Wilshire 5000 except
for the 500 stocks in the Standard & Poor's 500 Index.

RUSSELL 3000 STOCK INDEX--a diversified  portfolio of approximately 3,000 common
stocks  accounting for over 90% of the market value of publicly traded stocks in
the U.S.

RUSSELL 2000 STOCK INDEX--composed of the 2,000 smallest stocks contained in the
Russell  3000,  representing  approximately  7% of the Russell 3000 total market
capitalization.

RUSSELL  2000+ VALUE  INDEX--contains  stocks from the Russell 2000 Index with a
less-than-average growth orientation.

MORGAN  STANLEY  CAPITAL  INTERNATIONAL  EAFE  INDEX--is an  arithmetic,  market
value-weighted  average of the performance of over 900 securities  listed on the
stock exchanges of countries in Europe, Australasia and the Far East.

GOLDMAN SACHS 100  CONVERTIBLE  BOND  INDEX--currently  includes 71 bonds and 29
preferreds.   The  original  list  of  names  was  generated  by  screening  for
convertible  issues of $100  million or greater  in market  capitalization.  The
index is priced monthly.

SALOMON BROTHERS GNMA  INDEX--includes  pools of mortgages originated by private
lenders and guaranteed by the mortgage pools of the Government National Mortgage
Association.

SALOMON BROTHERS HIGH-GRADE  CORPORATE BOND  INDEX--consists of publicly issued,
non-convertible  corporate bonds rated AA or AAA. It is a value-weighted,  total
return index, including  approximately 800 issues with maturities of 12 years or
greater.

LEHMAN  LONG-TERM  TREASURY BOND INDEX--is a market weighted index that contains
individually  priced U.S.  Treasury  securities  with maturities of ten years or
greater.

MERRILL LYNCH CORPORATE & GOVERNMENT BOND--consists of over 4,500 U.S. Treasury,
Agency and investment grade corporate bonds.

LEHMAN   CORPORATE   (BAA)  BOND   INDEX--all   publicly   offered   fixed-rate,
nonconvertible  domestic  corporate bonds rated Baa by Moody's,  with a maturity
longer  than one year and with more than $100  million  outstanding.  This index
includes over 1,500 issues.

LEHMAN  BROTHERS  LONG-TERM  CORPORATE  BOND  INDEX--is  a subset of the  Lehman
Corporate  Bond Index  covering  all  corporate,  publicly  issued,  fixed-rate,
nonconvertible  U.S.  debt issues rated at least Baa, with at least $100 million
principal outstanding and maturity greater than ten years.

BOND BUYER  MUNICIPAL BOND INDEX--is a yield index on current coupon  high-grade
general obligation municipal bonds.

STANDARD & POOR'S PREFERRED INDEX--is a yield index based upon the average yield
of four high-grade, non-callable preferred stock issues.

NASDAQ INDUSTRIAL INDEX--is composed of more than 3,000 industrial issues. It is
a  value-weighted  index  calculated  on price  change only and does not include
income.

COMPOSITE  INDEX--70%  Standard  & Poor's  500 Index and 30%  NASDAQ  Industrial
Index.

COMPOSITE  INDEX--65%  Standard  & Poor's  500  Index and 35%  Lehman  Long-Term
Corporate AA or Better Bond Index.


                                    B-23
<PAGE>

COMPOSITE  INDEX--65%  Lehman Long-Term  Corporate AA or Better Bond Index and a
35% weighting in a blended equity  composite (75% Standard & Poor's/BARRA  Value
Index,  12.5%  Standard  & Poor's  Utilities  Index and 12.5%  Standard & Poor's
Telephone Index).

LEHMAN  LONG-TERM  CORPORATE AA OR BETTER BOND  INDEX--consists  of all publicly
issued,  fixed  rate,  nonconvertible   investment  grade,   dollar-denominated,
SEC-registered corporate debt rated AA or AAA.

LEHMAN  BROTHERS  AGGREGATE BOND INDEX--is a market weighted index that contains
individually priced U.S. Treasury,  agency, corporate, and mortgage pass-through
securities  corporate rated Baa-or better.  The Index has a market value of over
$5 trillion.

LEHMAN BROTHERS MUTUAL FUND SHORT (1-5) GOVERNMENT/CORPORATE  INDEX--is a market
weighted index that contains  individually  priced U.S.  Treasury,  agency,  and
corporate investment grade bonds rated BBB-or better with maturities between one
and five years. The index has a market value of over $1.6 trillion.

LEHMAN BROTHERS MUTUAL FUND INTERMEDIATE (5-10) GOVERNMENT/CORPORATE INDEX--is a
market weighted index that contains  individually priced U.S. Treasury,  agency,
and corporate  securities  rated BBB-or better with maturities  between five and
ten years. The index has a market value of over $800 billion.

LEHMAN  BROTHERS  LONG (10+)  GOVERNMENT/CORPORATE  INDEX--is a market  weighted
index that contains  individually  priced U.S.  Treasury,  agency, and corporate
securities rated BBB-or better with maturities greater than ten years. The index
has a market value of over $1.1 trillion.

LIPPER SMALL COMPANY GROWTH FUND AVERAGE--the  average performance of 25 largest
small  company  growth  funds as defined by Lipper Inc.  Lipper  defines a small
company growth fund as a fund that by prospectus or portfolio  practice,  limits
its investments to companies on the basis of the size of the company.  From time
to time, Vanguard may advertise using the average performance and/or the average
expense ratio of the small company  growth funds.  (This fund category was first
established  in 1982.  For years prior to 1982,  the results of the Lipper Small
Company  Growth  category  were  estimated  using the  returns of the Funds that
constituted the Group at its inception.)

LIPPER BALANCED FUND  AVERAGE--an  industry  benchmark of average balanced funds
with similar investment objectives and policies, as measured by Lipper Inc.

LIPPER  NON-GOVERNMENT  MONEY  MARKET FUND  AVERAGE--an  industry  benchmark  of
average non-government money market funds with similar investment objectives and
policies, as measured by Lipper Inc.

LIPPER  GOVERNMENT MONEY MARKET FUND AVERAGE--an  industry  benchmark of average
government money market funds with similar  investment  objectives and policies,
as measured by Lipper Inc.

























                                                             SAI023-12/17/ 1999

                                      B-25

<PAGE>


                                     PART C


                              VANGUARD WORLD FUNDS
                               OTHER INFORMATION


ITEM 23. EXHIBITS

EXHIBITS   DESCRIPTION
- --------   -----------
(a)    Declaration of Trust*
(b)    By-Laws*
(c)    Reference is made to Articles III and V of the Registrant's Declaration
       of Trust
(d)    Investment Advisory Contracts*
(e)    Not applicable
(f)    Reference is made to the section entitled "Management of the Trust" in
       the Registrant's Statement of Additional Information
(g)    Custodian Agreement*
(h)    Amended and Restated Funds' Service Agreement*
(i)    Legal Opinion*
(j)    Consent of Independent Accountants**
(k)    Not Applicable
(l)    Not Applicable
(m)    Not Applicable
(n)    Not Applicable
(o)    Not Applicable

 *Filed Previously
 **Filed Herewith

ITEM 24. PERSONS CONTROLLED BY OR UNDER COMMON CONTROL WITH REGISTRANT

Registrant is not controlled by or under common control with any person.


ITEM 25. INDEMNIFICATION

The  Registrant's   organizational  documents  contain  provisions  indemnifying
Trustees and officers  against  liability  incurred in their official  capacity.
Article VII,  Section 2 of the Declaration of Trust provides that the Registrant
may  indemnify  and hold  harmless  each and every  Trustee and officer from and
against  any and all  claims,  demands,  costs,  losses,  expenses,  and damages
whatsoever  arising out of or related to the performance of his or her duties as
a Trustee or officer.  However,  this  provision does not cover any liability to
which a Trustee  or  officer  would  otherwise  be  subject by reason of willful
misfeasance,  bad faith,  gross negligence,  or reckless disregard of the duties
involved  in  the  conduct  of  his or her  office.  Article  VI of the  By-Laws
generally provides that the Registrant shall indemnify its Trustees and officers
from  any  liability  arising  out of  their  past or  present  service  in that
capacity.  Among other things,  this provision excludes any liability arising by
reason of willful  misfeasance,  bad faith,  gross  negligence,  or the reckless
disregard  of the duties  involved in the conduct of the  Trustee's or officer's
office with the Registrant.


ITEM 26. BUSINESS AND OTHER CONNECTIONS OF INVESTMENT ADVISER

Lincoln  Capital  Management   Company  (Lincoln),   is  an  investment  adviser
registered  under the Investment  Advisers Act of 1940, as amended (the Advisers
Act).  The list  required by this Item 26 of officers and  directors of Lincoln,
together  with  any  information  as to any  business  profession,  vocation  or
employment  of a  substantial  nature  engaged in by such officers and directors
during the past two years,  is  incorporated  herein by reference to Schedules B
and D of Form ADV filed by Lincoln  pursuant to the  Advisers  Act (SEC File No.
801-11417).

                                      C-1
<PAGE>


     Schroder  Investment  Management  North  America,  Inc.  (Schroder),  is an
investment  adviser  registered  under the  Investment  Advisers Act of 1940, as
amended (the  Advisers  Act).  The list required by this Item 26 of officers and
directors  of  Schroder,  together  with  any  information  as to  any  business
profession,  vocation or employment of a substantial  nature  engaged in by such
officers and  directors  during the past two years,  is  incorporated  herein by
reference  to  Schedules B and D of Form ADV filed by  Schroder  pursuant to the
Advisers Act (SEC File No. 801-15834).


ITEM 27. PRINCIPAL UNDERWRITERS

a.     Not Applicable
b.     Not Applicable
c.     Not Applicable

ITEM 28. LOCATION OF ACCOUNTS AND RECORDS


All accounts,  books and other documents required to be maintained by Section 31
(a) of the 1940 Act and the Rules  thereunder  will be maintained at the offices
of  Registrant;  Registrant's  Transfer  Agent,  The Vanguard  Group,  Inc., 100
Vanguard   Boulevard,   Malvern,   Pennsylvania   19355;  and  the  Registrant's
custodians, State Street Bank and Trust Company, Boston, Massachusetts,  and The
Chase Manhattan Bank, N.A., New York, New York, and ..



ITEM 29. MANAGEMENT SERVICES

Other than as set forth under the description of The Vanguard Group in Part B of
this   Registration   Statement,   the   Registrant   is  not  a  party  to  any
management-related service contract.


ITEM 30. UNDERTAKINGS

Not Applicable





                                      C-2


<PAGE>


                                   SIGNATURES


Pursuant to the  requirements  of the  Securities Act of 1933 and the Investment
Company Act of 1940,  the  Registrant  hereby  certifies that it has duly caused
this  Registration  Statement  to be  signed on its  behalf by the  undersigned,
thereunto duly  authorized,  in the Town of Valley Forge and the Commonwealth of
Pennsylvania, on the 23rd day of February, 2000.


                                                  VANGUARD WORLD FUNDS

                                   BY:_____________(signature)________________

                                   (HEIDI STAM) JOHN J. BRENNAN* CHAIRMAN AND
                                              CHIEF EXECUTIVE OFFICER


     Pursuant  to  the   requirements  of  the  Securities  Act  of  1933,  this
Post-Effective  Amendment to the Registration Statement has been signed below by
the following persons in the capacities and on the date indicated:

SIGNATURE                     TITLE                              DATE
- --------------------------------------------------------------------------------



By:/S/ JOHN J. BRENNAN        President, Chairman, Chief      February 23, 2000
   ---------------------------Executive Officer, and Trustee
       (Heidi Stam)
      John J. Brennan*


By:/S/ JOANN HEFFERNAN HEISEN Trustee                         February 23, 2000
   ---------------------------
       (Heidi Stam)
     JoAnn Heffernan Heisen*


By:/S/ BRUCE K. MACLAURY      Trustee                         February 23, 2000
   ---------------------------
       (Heidi Stam)
      Bruce K. MacLaury*


By:/S/ BURTON G. MALKIEL      Trustee                         February 23, 2000
   ---------------------------
       (Heidi Stam)
       Burton G. Malkiel*



By:/S/ ALFRED M. RANKIN, JR.  Trustee                         February 23, 2000
   ---------------------------
       (Heidi Stam)
     Alfred M. Rankin, Jr.*


By:/S/ JOHN C. SAWHILL        Trustee                         February 23, 2000
   ---------------------------
       (Heidi Stam)
      John C. Sawhill*


By:/S/ JAMES O. WELCH, JR.    Trustee                         February 23, 2000
   ---------------------------
       (Heidi Stam)
     James O. Welch, Jr.*



By:/S/ J. LAWRENCE WILSON     Trustee                         February 23, 2000
   ---------------------------
       (Heidi Stam)
     J. Lawrence Wilson*



By:/S/ THOMAS J. HIGGINS      Treasurer and Principal         February 23, 2000
   ---------------------------
       (Heidi Stam)           Financial Officer and Principal
      Thomas J. Higgins*      Accounting Officer




*By Power of  Attorney.  See File Number  33-4424,  filed on January  25,  1999.
Incorporated by Reference.



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