Exhibit 5.1

[LETTERHEAD OF BROBECK PHLEGER & HARRISON LLP]

April 12, 2002

ValueClick, Inc.
4360 Park Terrace Drive, Suite 100
Westlake Village, California 91361

Re: ValueClick, Inc. Registration Statement on Form S-4
for 45,188,527 Shares of Common Stock                                

Ladies and Gentlemen:

        We have acted as counsel to ValueClick, Inc., a Delaware corporation (the "Company"), in connection with the proposed issuance and sale by the Company of up to 45,188,527 shares of the Company's Common Stock (the "Shares") pursuant to the Company's Registration Statement on Form S-4 (the "Registration Statement") filed with the Securities and Exchange Commission under the Securities Act of 1933, as amended (the "Act").

        This opinion is being furnished in accordance with the requirements of Item 21(a) of Form S-4 and Item 601(b)(5)(i) of Regulation S-K.

        We have reviewed the Company's charter documents and the corporate proceedings taken by the Company in connection with the issuance and sale of the Shares. Based on such review, and assuming the approval of ValueClick Proposal Number Two (as described in the Registration Statement) by the Company's stockholders to amend and restate the Company's Amended and Restated Certificate of Incorporation to increase the authorized number of shares of common stock from 100,000,000 to 500,000,000 shares, we are of the opinion that the Shares have been duly authorized, and if, as and when issued in accordance with the Registration Statement and the related prospectus (as amended and supplemented through the date of issuance) will be legally issued, fully paid and nonassessable.

        We consent to the filing of this opinion letter as Exhibit 5.1 to the Registration Statement and to the reference to this firm under the caption "Legal Matters" in the prospectus which is part of the Registration Statement. In giving this consent, we do not thereby admit that we are within the category of persons whose consent is required under Section 7 of the Act, the rules and regulations of the Securities and Exchange Commission promulgated thereunder, or Item 509 of Regulation S-K.

        This opinion letter is rendered as of the date first written above and we disclaim any obligation to advise you of facts, circumstances, events or developments which hereafter may be brought to our attention and which may alter, affect or modify the opinion expressed herein. Our opinion is expressly limited to the matters set forth above and we render no opinion, whether by implication or otherwise, as to any other matters relating to the Company or the Shares.

Very truly yours,

/s/ BROBECK, PHLEGER & HARRISON LLP