Exhibit 5.1

                               DAVIS & GILBERT LLP
                                  1740 Broadway
                            New York, New York 10019

                                                                   April 8, 2003

Omnicom Group Inc.
437 Madison Avenue
New York, NY 10022

                     Re: Registration Statement on Form S-3

Gentlemen:

      In our capacity as counsel to Omnicom Group Inc., a New York corporation
(the "Company"), we have been asked to render this opinion in connection with a
registration statement on Form S-3 (the "Registration Statement") being filed by
the Company contemporaneously herewith on behalf of the selling shareholders
named therein (the "Selling Shareholders") with the Securities and Exchange
Commission under the Securities Act of 1933, as amended, covering an aggregate
of 224,408 shares of common stock, $0.15 par value, of the Company being offered
for the respective accounts of the Selling Shareholders (the "Selling
Shareholders' Shares").

      In that connection, we have examined the Certificate of Incorporation and
the By-laws, both as amended, of the Company, the Registration Statement, the
corporate proceedings relating to the issuance of the Selling Shareholders'
Shares, and such other instruments and documents as we deemed relevant under the
circumstances.

      In making the aforesaid examinations, we have assumed the genuineness of
all signatures and the conformity to original documents of all copies furnished
to us as original or photostatic copies. We have also assumed that the corporate
records furnished to us by the Company include all corporate proceedings taken
by the Company to date.

      Based upon and subject to the foregoing, we are of the opinion that the
Selling Shareholders' Shares when sold by the Selling Shareholders will be
legally issued, fully paid and nonassessable.

      We hereby consent to the use of our opinion as herein set forth as an
exhibit to the Registration Statement and to the use of our name under the
caption "Legal Matters" in the Prospectus forming part of the Registration
Statement.

                                              Very truly yours,

                                              /s/ Davis & Gilbert LLP