Exhibit 5.1

                               Omnicom Group Inc.

                               437 Madison Avenue
                            New York, New York 10022
                                TEL 212 415-3600

                                November 15, 2000

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

            Re: Registration Statement on Form S-3

Dear Sirs:

      This opinion is furnished in connection with the preparation of the
Registration Statement on Form S-3 (the "Registration Statement") filed with the
Securities and Exchange Commission (the "Commission") by Omnicom Group Inc., a
New York corporation (the "Company"), and Omnicom Capital Trust I, Omnicom
Capital Trust II and Omnicom Capital Trust III, each a statutory business trust
formed under the laws of the State of Delaware (individually, the "Trust" and
collectively, the "Trusts"), on October 4, 2000. The Registration Statement
relates to the issuance and sale from time to time pursuant to Rule 415 of the
General Rules and Regulations promulgated under the Securities Act of 1933, as
amended (the "Securities Act") of the following securities with an aggregate
initial public offering price of up to $750,000,000: (i) common stock, par value
$.15 per share of the Company ("Common Stock"), (ii) one or more series of
preferred stock, par value $1.00 per share of the Company ("Preferred Stock"),
interests in which may be represented by depositary shares of the Company
("Depositary Shares"), (iii) one or more series of debt securities of the
Company ("Debt Securities"), consisting of debentures, notes and/or other
unsecured evidences of indebtedness, which may be unsubordinated ("Senior Debt
Securities") or subordinated ("Subordinated Debt Securities" and "Junior
Subordinated Debt Securities") to certain other obligations of the Company,
(iv) warrants to purchase Debt Securities under the Senior Indenture and
Subordinated Indenture (as hereinafter defined), Preferred Stock or Common Stock
of the Company ("Warrants"), (v) Trust Preferred Securities of the Trusts
("Trust Preferred Securities"), and (vi) guarantees by the Company of the Trust
Preferred Securities (individually, "Trust Guarantee," and collectively, "Trust
Guarantees," and together with the Common Stock, Preferred Stock, Depositary
Shares, Debt Securities and Warrants, "Securities").

      The Senior Debt Securities may be issued under a senior indenture in the
form incorporated by reference as an exhibit to the Registration Statement, as
amended or supplemented from time to time (the "Senior Indenture"), proposed to
be entered into between the Company and one or more trustees chosen by the
Company and qualified to act as such under the Trust Indenture Act of 1939, as
amended ( the "TIA") (any such


Omnicom Group Inc.
November 15, 2000
Page 2


trustee, the "Senior Indenture Trustee"). The Subordinated Debt Securities may
be issued under a subordinated indenture in the form incorporated by reference
as an exhibit to the Registration Statement, as amended or supplemented from
time to time (the "Subordinated Indenture"), proposed to be entered into between
the Company and one or more trustees chosen by the Company and qualified to act
as such under the TIA (any such trustee, the "Subordinated Indenture Trustee").
The Junior Subordinated Debt Securities may be issued under a junior
subordinated indenture in the form filed as an exhibit to the Registration
Statement, as amended or supplemented from time to time (the "Junior
Subordinated Indenture"), proposed to be entered into between the Company and
one or more trustees chosen by the Company and qualified to act as such under
the TIA (any such trustee, the "Junior Subordinated Indenture Trustee," and,
together with the Senior Indenture Trustee and the Subordinated Indenture
Trustee, the "Trustees"). The Senior Indenture, the Subordinated Indenture and
the Junior Subordinated Indenture are sometimes hereinafter referred to
individually as the "Indenture" and collectively as the "Indentures." The Trust
Preferred Securities will be issued by each Trust pursuant to an amended and
restated trust agreement in the form filed as an exhibit to the Registration
Statement, as amended or supplemented from time to time (the "Trust Agreement"),
proposed to be entered into between the Company, as sponsor, a Property Trustee
to be chosen by the Company and qualified to act as such under the TIA, Chase
Manhattan Bank, National Association, as Delaware Trustee, and the
Administrative Trustees named therein, and each Trust Guarantee will be issued
pursuant to a guarantee agreement in the form filed as an exhibit to the
Registration Statement, as amended or supplemented from time to time (the
"Guarantee Agreement"), proposed to be entered into between the Company and the
trustee named therein.

      This opinion is delivered in accordance with the requirements of Item
601(b)(5) of Regulation S-K under the Securities Act.

      As General Counsel and Secretary of the Company, I have examined (i) the
form of Registration Statement relating to the Securities and the Trust
Preferred Securities; (ii) the form of Senior Indenture; (iii) the form of
Subordinated Indenture; (iv) the form of Junior Subordinated Indenture; (v) the
Amended and Restated Trust Agreement; (vi) the Guarantee Agreement; (vii) the
Certificate of Incorporation of the Company, as amended and currently in effect
(the "Certificate of Incorporation"); (viii) the By-Laws of the Company as
currently in effect (the "By-Laws"); and (ix) resolutions adopted by the Board
of Directors of the Company (the "Board") relating to the issuance of the
Securities (the "Board Resolutions"). I have also examined originals or copies,
certified or otherwise identified to my satisfaction, of such records of the
Company and such agreements, certificates of public officials, certificates of
officers or other representatives of the Company and others, and such other
documents, certificates and records as I have deemed necessary or appropriate as
a basis for the opinions set forth herein.

      In my capacity as General Counsel and Secretary, I am familiar with the
proceedings taken and proposed to be taken by the Company in connection with the


Omnicom Group Inc.
November 15, 2000
Page 3


authorization and issuance of the Securities. For purposes of this opinion, I
have assumed that such proceedings will be timely and properly completed, in
accordance with all requirements of applicable federal and New York laws, in the
manner presently proposed.

      In my examination, I have assumed the legal capacity of all natural
persons, the genuineness of all signatures, the authenticity of all documents
submitted to me as originals, the conformity to original documents of all
documents submitted to me as certified, conformed or photostatic copies and the
authenticity of the originals of such latter documents. In making my examination
of documents executed by parties other than the Company, I have assumed that
such parties had the power, corporate or other, to enter into and perform all
their obligations thereunder and have also assumed the due authorization by all
requisite action, corporate or other, and execution and delivery by such parties
of such documents and the validity and binding effect thereof. As to any facts
material to the opinions expressed herein which were not independently
established or verified, I have relied upon oral or written statements and
representations of officers and other representatives of the Company and others.
I have assumed that (1) the Senior Indenture, the Subordinated Indenture and the
Junior Subordinated Indenture each will be duly authorized, executed and
delivered by the respective Trustees, and that any Debt Securities that may be
issued will be manually signed by duly authorized officers of the applicable
Trustee; (2) any Trust Agreement and Guarantee Agreement, respectively, will be
duly authorized, executed and delivered by the applicable Trustees; and (3) any
Depositary Agreement and any Warrant Agreement (each as hereinafter defined)
will be duly authorized, executed and delivered by the Depositary and the
Warrant Agent, respectively, and that the Warrants will be duly signed by the
Depositary and the Warrant Agent.

      I am admitted to the Bar in the State of New York, and I do not express
any opinion as to the laws of any jurisdiction other than the corporate laws of
the State of New York and the laws of the United States of America to the extent
referred to specifically herein. The Securities may be issued from time to time
on a delayed or continuous basis, but this opinion is limited to the laws,
including the rules and regulations thereunder, as in effect on the date hereof.

      Based upon and subject to the foregoing, I am of the opinion that:

      1. With respect to any offering of Common Stock (the "Offered Common
Stock"), when (i) the Registration Statement, as finally amended (including all
necessary post-effective amendments) has become effective; (ii) an appropriate
Prospectus Supplement with respect to the Offered Common Stock has been
prepared, delivered and filed in compliance with the Securities Act and the
applicable rules and regulations thereunder; (iii) if the Offered Common Stock
is to be sold pursuant to a firm commitment underwritten offering, the
underwriting agreement with respect to the Offered Common Stock in the form to
be filed as an exhibit to the Registration Statement or any post-effective
amendment thereto, or incorporated by reference therein, has been

Omnicom Group Inc.
November 15, 2000
Page 4


duly authorized, executed and delivered by the Company and the other parties
thereto; (iv) the Board, including any appropriate committee appointed thereby,
and appropriate officers of the Company have taken all necessary corporate
action to approve the issuance of the Offered Common Stock and related matters;
(v) the terms of the issuance and sale of the Offered Common Stock have been
duly established in conformity with the Certificate of Incorporation and the
By-Laws so as not to violate any applicable law, the Certificate of
Incorporation or the By-Laws or result in a default under or breach of any
agreement or instrument binding upon the Company and so as to comply with any
restriction imposed by any court or governmental body having jurisdiction over
the Company; and (vi) certificates representing the shares of the Offered Common
Stock have been duly executed, countersigned, registered and delivered upon
payment of the agreed-upon consideration therefor and have been duly issued and
sold in accordance with the underwriting agreement with respect to the Offered
Common Stock or any other duly authorized, executed and delivered, applicable,
valid and binding purchase agreement, or as otherwise contemplated by the
Registration Statement or any post-effective amendment thereto, and any
Prospectus Supplement relating thereto, the shares of the Offered Common Stock
(including any Offered Common Stock duly issued upon conversion or exchange of
any Debt Securities or shares of Preferred Stock convertible or exchangeable
into Common Stock or upon exercise of any Warrants exercisable for Common Stock)
will be duly authorized, validly issued, fully paid and nonassessable, provided
that the consideration therefor is not less than the par value thereof.

      2. With respect to any offering of any series of Preferred Stock (the
"Offered Preferred Stock"), when (i) the Registration Statement, as finally
amended (including all necessary post-effective amendments), has become
effective; (ii) an appropriate Prospectus Supplement with respect to the Offered
Preferred Stock has been prepared, delivered and filed in compliance with the
Securities Act and the applicable rules and regulations thereunder; (iii) if the
Offered Preferred Stock is to be sold pursuant to a firm commitment underwritten
offering, the underwriting agreement with respect to the Offered Preferred Stock
in the form to be filed as an exhibit to the Registration Statement or any
post-effective amendment thereto, or incorporated by reference therein, has been
duly authorized, executed and delivered by the Company and the other parties
thereto; (iv) the Board, including any appropriate committee appointed thereby,
and appropriate officers of the Company have taken all necessary corporate
action to approve the issuance and terms of the shares of the Offered Preferred
Stock and related matters, including the adoption of a Certificate of Amendment
to the Certificate of Incorporation in accordance with the applicable provisions
of Business Corporation Law of the State of New York (the "Certificate of
Amendment"); (v) the Certificate of Amendment has been duly filed with the
Secretary of State of the State of New York; (vi) the terms of the Offered
Preferred Stock and of its issuance and sale have been duly established in
conformity with the Certificate of Incorporation (including the Certificate of
Amendment relating to the Offered Preferred Stock) and the By-Laws so as not to
violate any applicable law, the Certificate of Incorporation or the By-Laws or
result in default under or breach of any agreement or instrument binding upon
the Company and so as to comply


Omnicom Group Inc.
November 15, 2000
Page 5


with any requirement or restriction imposed by any court or governmental body
having jurisdiction over the Company; and (vii) certificates representing the
shares of the Offered Preferred Stock have been duly executed, countersigned,
registered and delivered upon payment of the agreed-upon consideration therefor
and have been duly issued and sold in accordance with the underwriting agreement
with respect to the Offered Preferred Stock or any other duly authorized,
executed and delivered, applicable, valid and binding purchase agreement, or as
otherwise contemplated by the Registration Statement or any post-effective
amendment thereto, and any Prospectus Supplement relating thereto, the shares of
the Offered Preferred Stock (including any Offered Preferred Stock duly issued
upon conversion or exchange of any Debt Securities convertible or exchangeable
into Preferred Stock or upon exercise of any Warrants exercisable for Preferred
Stock or upon surrender of any Depositary Shares in connection with the
withdrawal of Preferred Stock), will be duly authorized, validly issued, fully
paid and nonassessable, provided that the consideration therefor is not less
than the par value thereof.

      3. With respect to any offering of any series of Depositary Shares (the
"Offered Depositary Shares"), when (i) the Registration Statement, as finally
amended (including all necessary post-effective amendments), has become
effective; (ii) an appropriate Prospectus Supplement with respect to the Offered
Depositary Shares has been prepared, delivered and filed in compliance with the
Securities Act and the applicable rules and regulations thereunder; (iii) the
depositary agreement relating to the Offered Depositary Shares (the "Depositary
Agreement") in the form to be filed as an exhibit to the Registration Statement
or any post-effective amendment thereto, or incorporated by reference therein,
has been duly executed and delivered as contemplated by the Board Resolutions or
other action by the Board or a duly appointed committee thereof; (iv) if the
Offered Depositary Shares are to be sold pursuant to a firm commitment
underwritten offering, the underwriting agreement with respect to the Offered
Depositary Shares in the form to be filed as an exhibit to the Registration
Statement or any post-effective amendment thereto, or incorporated by reference
therein, has been duly authorized, executed and delivered by the Company and the
other parties thereto; (v) the Board, including any appropriate committee
appointed thereby, and appropriate officers of the Company have taken all
necessary corporate action to approve the issuance and terms of the Offered
Depositary Shares and related matters; (vi) the terms of the Offered Depositary
Shares and of their issuance and sale have been duly established in conformity
with the Depositary Agreement so as not to violate any applicable law, the
Certificate of Incorporation or the By-Laws or result in a default under or
breach of any agreement or instrument binding upon the Company and so as to
comply with any requirement or restriction imposed by any court or governmental
body having jurisdiction over the Company; (vii) the receipts for the Offered
Depositary Shares (the "Receipts") have been duly executed, countersigned,
registered and delivered in accordance with the Depositary Agreement relating to
such Offered Depositary Shares, and the Offered Depositary Shares have been duly
issued and sold in accordance with the Depositary Agreement, the underwriting
agreement with respect to the Offered Depositary Shares or any other duly
authorized, executed and delivered, applicable, valid


Omnicom Group Inc.
November 15, 2000
Page 6


and binding purchase agreement, or as otherwise contemplated by the Registration
Statement or any post-effective amendment thereto, and any Prospectus Supplement
relating thereto; and (viii) the Preferred Stock which is represented by the
Offered Depositary Shares is duly authorized, validly issued and delivered to
the Depositary in accordance with the laws of the State of New York, (1) the
Offered Depositary Shares will be valid and binding obligations of the Company,
enforceable against the Company in accordance with their terms, except to the
extent that enforcement thereof may be limited by (a) bankruptcy, insolvency,
reorganization, fraudulent transfer, moratorium or other similar laws now or
hereafter in effect relating to creditors' rights generally, (b) general
principles of equity (regardless of whether enforceability is considered in a
proceeding at law or in equity), and (c) public policy considerations which may
limit the rights of parties to obtain further remedies; and (2) when the
Receipts evidencing the Offered Depositary Shares are duly issued against the
deposit of the Preferred Stock in accordance with the Depositary Agreement, such
Receipts will be validly issued and will entitle the holders thereof to the
rights specified therein and in the Depositary Agreement.

      4. With respect to any offering of any series of Debt Securities (the
"Offered Debt Securities"), when (i) the Registration Statement, as finally
amended (including all necessary post-effective amendments), has become
effective; (ii) an appropriate Prospectus Supplement with respect to the Offered
Debt Securities has been prepared, delivered and filed in compliance with the
Securities Act and the applicable rules and regulations thereunder; (iii) if the
Offered Debt Securities are to be sold pursuant to a firm commitment
underwritten offering, the underwriting agreement with respect to the Offered
Debt Securities in the form to be filed as an exhibit to the Registration
Statement or any post-effective amendment thereto, or incorporated by reference
therein, has been duly authorized, executed and delivered by the Company and the
other parties thereto; (iv) the Board, including any appropriate committee
appointed thereby, and appropriate officers of the Company have taken all
necessary corporate action to approve the issuance and terms of the Offered Debt
Securities and related matters; (v) the terms of the Offered Debt Securities and
of their issuance and sale have been duly established in conformity with the
applicable Indenture so as not to violate any applicable law, the Certificate of
Incorporation or the By-Laws or result in a default under or breach of any
agreement or instrument binding upon the Company and so as to comply with any
requirement or restriction imposed by any court or governmental body having
jurisdiction over the Company; (vi) the applicable Indenture has been qualified
under the TIA and duly executed and delivered by the Company and the applicable
Trustee; and (vii) the Offered Debt Securities have been duly executed and
authenticated in accordance with the provisions of the applicable Indenture and
delivered to the purchasers thereof upon payment of the agreed-upon
consideration therefor and have been duly issued and sold in accordance with the
applicable Indenture and the underwriting agreement with respect to the Offered
Debt Securities or any other duly authorized, executed and delivered applicable
valid and binding purchase agreement, or as otherwise contemplated by the
Registration Statement, or any post-effective amendment thereto, and any
Prospectus Supplement relating thereto, the Offered Debt


Omnicom Group Inc.
November 15, 2000
Page 7


Securities (including any Offered Debt Securities, offered under the Senior
Indenture and Subordinated Indenture, duly issued upon conversion or exchange of
any shares of Preferred Stock convertible or exchangeable into such Debt
Securities or upon exercise of any Warrants exercisable for such Debt
Securities), will be valid and binding obligations of the Company, enforceable
against the Company in accordance with their terms, except to the extent that
enforcement thereof may be limited by (a) bankruptcy, insolvency,
reorganization, fraudulent transfer, moratorium or other similar laws now or
hereafter in effect relating to creditors' rights generally, (b) general
principles of equity (regardless of whether enforceability is considered in a
proceeding at law or in equity), and (c) public policy considerations which may
limit the rights of parties to obtain further remedies.

      5. With respect to any offering of any series of Warrants (the "Offered
Warrants"), when (i) the Registration Statement, as finally amended (including
all necessary post-effective amendments), has become effective; (ii) an
appropriate Prospectus Supplement with respect to the Offered Warrants has been
prepared, delivered and filed in compliance with the Securities Act and the
applicable rules and regulations thereunder; (iii) the warrant agreement
relating to the Offered Warrants (the "Warrant Agreement") in the form to be
filed as an exhibit to the Registration Statement or any post-effective
amendment thereto, or incorporated by reference therein, has been duly executed
and delivered as contemplated by the Board Resolutions or other action by the
Board or a duly appointed committee thereof; (iv) if the Offered Warrants are to
be sold pursuant to a firm commitment underwritten offering, the underwriting
agreement with respect to the Offered Warrants in the form to be filed as an
exhibit to the Registration Statement or any post-effective amendment thereto,
or incorporated by reference therein, has been duly authorized, executed and
delivered by the Company and the other parties thereto; (v) the Board, including
any appropriate committee appointed thereby, and appropriate officers of the
Company have taken all necessary corporate action to approve the issuance and
terms of the Offered Warrants and related matters; (vi) the terms of the Offered
Warrants and of their issuance and sale have been duly established in conformity
with the Warrant Agreement so as not to violate any applicable law, the
Certificate of Incorporation or the By-Laws or result in a default under or
breach of any agreement or instrument binding upon the Company and so as to
comply with any requirement or restriction imposed by any court or governmental
body having jurisdiction over the Company; and (vii) the Offered Warrants have
been duly executed, countersigned, registered and delivered and have been duly
issued and sold in accordance with the Warrant Agreement, the underwriting
agreement with respect to the Offered Warrants or any other duly authorized,
executed and delivered, applicable, valid and binding purchase agreement, or as
otherwise contemplated by the Registration Statement, or any post-effective
amendment thereto, and any Prospectus Supplement relating thereto, the Offered
Warrants will be valid and binding obligations of the Company, enforceable
against the Company in accordance with their terms, except to the extent that
enforcement thereof may be limited by (a) bankruptcy, insolvency,
reorganization, fraudulent transfer, moratorium or other similar laws now or
hereafter in effect relating to creditors' rights generally, (b) general
principles of equity (regardless of whether


Omnicom Group Inc.
November 15, 2000
Page 8


enforceability is considered in a proceeding at law or in equity), and (c)
public policy considerations which may limit the rights of parties to obtain
further remedies.

      6. With respect to any offering of any Trust Preferred Securities by a
Trust (the "Offered Trust Preferred Securities") and any Trust Guarantee by the
Company (the "Offered Trust Guarantee"), when (i) the Registration Statement, as
finally amended (including all necessary post-effective amendments), has become
effective; (ii) an appropriate Prospectus Supplement with respect to the Offered
Trust Preferred Securities and the Offered Trust Guarantee has been prepared,
delivered and filed in compliance with the Securities Act and the TIA and the
applicable rules and regulations thereunder; (iii) the Offered Trust Preferred
Securities have been executed, authenticated and delivered in accordance with
the terms of the applicable Trust Agreement; (iv) the applicable Trust Agreement
has been duly executed and delivered by the Company and the other parties
thereto; (v) if the Offered Trust Preferred Securities are to be sold pursuant
to a firm commitment underwritten offering, the underwriting agreement with
respect to the Offered Trust Preferred Securities in the form to be filed as an
exhibit to the Registration Statement or any post-effective amendment thereto,
or incorporated by reference therein, has been duly authorized, executed and
delivered by the Company and the other parties thereto; (vi) the Board,
including any appropriate committee appointed thereby, and appropriate officers
of the Company have taken all necessary corporate action to approve the issuance
and terms of the Offered Trust Guarantee and related matters; (vii) the terms of
the Offered Trust Guarantee have been duly established in conformity with the
applicable Indenture and Guarantee Agreement so as not to violate any applicable
law, the Certificate of Incorporation or the By-Laws or result in a default
under or breach of any agreement or instrument binding upon the Company and so
as to comply with any requirement or restriction imposed by any court or
governmental body having jurisdiction over the Company; (viii) the Offered Trust
Preferred Securities have been duly executed and authenticated in accordance
with the provisions of the applicable Trust Agreement and delivered to the
purchasers thereof upon payment of the agreed-upon consideration therefor and
have been duly issued and sold in accordance with the applicable Trust Agreement
and the underwriting agreement with respect to the Offered Trust Preferred
Securities or any other duly authorized, executed and delivered applicable valid
and binding purchase agreement, or as otherwise contemplated by the Registration
Statement, or any post-effective amendment thereto, and any Prospectus
Supplement relating thereto; and (ix) the Offered Trust Guarantee has been duly
executed and authenticated in accordance with the provisions of the applicable
Guarantee Agreement, the Offered Trust Guarantee will be a valid and binding
obligation of the Company, enforceable against the Company in accordance with
its terms, except to the extent that enforcement thereof may be limited by (a)
bankruptcy, insolvency, reorganization, fraudulent transfer, moratorium or other
similar laws now or hereafter in effect relating to creditors' rights generally,
(b) general principles of equity (regardless of whether enforceability is
considered in a proceeding at law or in equity), and (c) public policy
considerations which may limit the rights of parties to obtain further remedies.


Omnicom Group Inc.
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Page 9


      I hereby consent to the filing of this opinion with the Commission as
Exhibit 5.1 to the Registration Statement. I also consent to the reference to my
name as general counsel under the heading "Legal Matters" in the Registration
Statement. In giving this consent, I do not thereby admit that I am in the
category of persons whose consent is required under Section 7 of the Securities
Act or the rules and regulations of the Commission promulgated thereunder.

                                         Very truly yours,

                                         /s/ Barry J. Wagner