<PAGE>
As filed pursuant to Rule 424(b)(3)
Registration No. 333-78959
PROSPECTUS SUPPLEMENT DATED JANUARY 10, 1999
TO PROSPECTUS DATED AUGUST 18, 1999
DOUBLECLICK INC.
$250,000,000 4.75% Convertible Subordinated Notes due 2006
(Interest Payable March 15 and September 15)
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3,030,303 Shares of Common Stock
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The information contained in the table appearing under the heading
"Selling Securityholders" on pages 40 - 42 of the Prospectus is hereby amended
to add the following information:
<TABLE>
<CAPTION>
Principal Shares of
Amount of Percentage of Common Stock
Notes that Notes that May be
Name of Selling Securityholder May be Sold Outstanding Sold
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<S> <C> <C> <C>
Island Holdings .............................. $ 10,000 * % 121
Lincoln National Convertible Securities Fund.. 1,200,000 * 14,545
Morgan Stanley Dean Witter Convertible
Securities Trust............................ 250,000 * 3,030
Sage Capital.................................. 1,500,000 * 18,181
</TABLE>
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* less than one percent
The information contained in the table appearing under the heading
"Selling Securityholders" on pages 40 - 42 of the Prospectus with respect to the
Selling Securityholders named below is hereby deleted and restated with the
following information:
<TABLE>
<CAPTION>
Principal Shares of
Amount of Percentage of Common Stock
Notes that Notes that May be
Name of Selling Securityholder May be Sold Outstanding Sold
- ---------------------------------------------------------------------------------------------------------------------------------
<S> <C> <C> <C>
JMG Convertible Investments, L.P. ...... $ 6,500,000 2.6% 78,787
Triton Capital Investments, Ltd. ....... 11,470,000 4.6 139,030
</TABLE>
