Exhibit 8.1
                                           February 9, 2001

Omnicom Group Inc.
437 Madison Avenue
New York NY 10022

Ladies and Gentlemen:

      We have acted as counsel to Omnicom Group Inc. (the "Company") in
connection with the preparation and filing of a Registration Statement on Form
S-3 (the "Registration Statement") pursuant to the Securities Act of 1933, as
amended (the "Securities Act"), relating to the registration for resale under
the Securities Act of $750,000,000 aggregate issue price of the Company's Liquid
Yield Option(TM) Notes due 2031 (the "Notes") which may be converted in certain
cases into shares of the Company's common stock.

      In connection with our opinion we have reviewed the Registration
Statement, including the exhibits thereto, and such other documents, records and
instruments as we have deemed necessary or appropriate for purposes of this
opinion.

      This opinion is based upon current provisions of the Internal Revenue Code
of 1986, as amended, and the legislative history thereto and Treasury
Regulations issued thereunder, current administrative rulings and practices of
the Internal Revenue Service and judicial decisions, all of which are subject to
change or differing interpretation, possibly with retroactive effect, at any
time.

      Based upon and subject to the foregoing, we hereby confirm that the
discussion set forth in the Registration Statement under the headings
"Summary-Tax Original Issue Discount" and "Federal Income Tax Considerations,"
subject to the qualifications set forth therein, to the extent it states matters
of law, summaries of legal matters, or legal conclusions with respect thereto
under the laws of the United States, is a fair summary in all material respects.

      We hereby consent to the filing of this opinion as an exhibit to the
Registration Statement and to the use of our name under the heading "Federal
Income Tax Considerations" in the Registration Statement. In giving this
consent, we do not thereby admit that we are included in the category of persons
whose consent is required under Section 7 of the Securities Act or the rules and
regulations promulgated thereunder.

                                       Very truly yours,

                                       /s/ Jones Day Reavis & Pogue
                                       ----------------------------
                                       Jones Day Reavis & Pogue