<PAGE>
As filed pursuant to Rule 424(b)(3) and (c)
Registration No. 333-31826
PROSPECTUS SUPPLEMENT DATED JULY 21, 2000
TO PROSPECTUS DATED MARCH 16, 2000
DOUBLECLICK INC.
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913,284 Shares of Common Stock
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This Prospectus Supplement supplements our Prospectus dated March 16, 2000
relating to the public offering, which is not being underwritten, and sale by
certain of our shareholders or by pledgees, donees, transferees or other
successors in interest that receive such shares as a gift, partnership
distribution or other non-sale related transfer (the "Selling Stockholders") of
up to 913,284 shares of our Common Stock, who received such shares in connection
with our acquisitions of Businesslink Incorporated and DoubleClick Scandinavia
AB. This Prospectus Supplement should be read in conjunction with the
Prospectus, and this Prospectus Supplement is qualified by reference to the
Prospectus except to the extent that information herein contained supersedes the
information contained in the Prospectus. Capitalized terms used in this
Prospectus Supplement and not otherwise defined herein have the meanings
specified in the Prospectus.
The information contained in the table appearing under the heading "Selling
Stockholders" on pages 19-21 of the Prospectus is hereby amended to add the
following information:
<TABLE>
<CAPTION>
Number of Shares Number of Shares
Beneficially Registered for
Name Owned Sale Hereby
---------------------------------------------------------------------------------
<S> <C> <C>
LBD Ledstiernan Business Development Ltd.... 28,155 23,182
</TABLE>
The information contained in the table appearing under the heading "Selling
Stockholders" on pages 19-21 of the Prospectus with respect to the Selling
Stockholders named below is hereby deleted and restated with the following
information:
<TABLE>
<CAPTION>
Number of Shares Number of Shares
Beneficially Registered for
Name Owned Sale Hereby
-------------------------------------------------------------------------------------
<S> <C> <C>
Mats Sundstrom .................................... 68,502 56,402
Ledstiernan BV .................................... 40,422 33,282
Celsia S.A. ....................................... 27,209(7) 27,160
Ledstiernan Investment Ltd ....................... 28,155 23,182
Minvest .......................................... 11,824 9,736
Sven Goran Arvinius(2) ............................ 2,719(8) 5,666
Other holders of shares of our common stock(5) .... 16,240
</TABLE>
(2) This stockholder is currently a sales director of DoubleClick Sandinavia.
(5) Information about other selling stockholders will be set forth in
additional prospectus supplements, if required.
(7) Excludes 5,000 shares of our common stock previously sold by this
stockholder under the prospectus dated March 16, 2000.
(8) Excludes 4,000 shares of our common stock previously sold by this
stockholder under the prospectus dated March 16, 2000.
