Document:

Exhibit 4.1

                                                               Execution Version

                          SECOND SUPPLEMENTAL INDENTURE

      This SECOND SUPPLEMENTAL INDENTURE (the "Supplemental Indenture") dated as
of August 12, 2004 among OMNICOM GROUP INC., a New York corporation (the
"Company"), OMNICOM CAPITAL INC., a Connecticut corporation ("OCI"), OMNICOM
FINANCE INC., a Delaware corporation ("OFI" and together with the Company and
OCI, the "Issuers"), and JPMORGAN CHASE BANK, as trustee under the indenture
referred to below (the "Trustee").

                              W I T N E S S E T H:

      WHEREAS, the Issuers and the Trustee have heretofore executed and
delivered to the Trustee an Indenture dated March 6, 2002, as amended by the
First Supplemental Indenture, dated February 13, 2003 (as so amended, the
"Indenture"), providing for the issuance of an aggregate principal amount of up
to $900,000,000 of Zero Coupon Zero Yield Convertible Notes due 2032 (the
"Securities"), all of which have been issued and $892,273,000 of which are
outstanding on the date hereof;

      WHEREAS, the Issuers desire (i) to surrender their right to pay
Securityholders who are converting their Securities pursuant to Article 10 of
the Indenture with shares of Common Stock, (ii) to surrender their right to
designate a financial institution to deliver shares of Common Stock upon
conversion pursuant to Article 10 of the Indenture and (iii) to modify the
method by which Contingent Cash Interest is determined;

      WHEREAS, it is in the best interests of the Issuers to surrender such
rights and to modify the method by which Contingent Cash Interest is determined;

      WHEREAS, Sections 9.02(2) and 9.02(5) of the Indenture provides that the
Issuers and the Trustee may amend or supplement the Indenture only with the
consent of affected Securityholders;

      WHEREAS, all Securityholders have consented to this Supplemental Indenture
and all outstanding Notes shall be bound by it;

      WHEREAS, an Opinion of Counsel has been delivered to the Trustee under
Section 9.02; and

      WHEREAS, pursuant to Sections 9.02 and 9.06 of the Indenture, the Trustee
and the Company are authorized to execute and deliver this Supplemental
Indenture;

      NOW THEREFORE, for good and valuable consideration, the receipt of which
is hereby acknowledged, the Issuers and the Trustee mutually covenant and agree
for the equal and ratable benefit of the holders of the Securities as follows:

1.    Definitions. All capitalized terms used but not defined herein shall have
      the meanings given to such terms set forth in the Indenture.

2.    Amendments. The Indenture be and hereby is amended as follows:

<PAGE>

      2.1   Section 10.02 of the Indenture is hereby amended and restated in its
            entirety to read as follows:

            "SECTION 10.02 Conversion Procedure.

      To convert a Security a Holder must satisfy the requirements in paragraph
9 of the Securities. The date on which the Holder satisfies all those
requirements is the conversion date (the "Conversion Date").

      As soon as practicable following the Conversion Date, the Issuers will
deliver, directly or through the Conversion Agent, an amount in cash (the "Cash
Amount") equal to the Initial Principal Amount at Maturity of the Securities
surrendered for conversion. The difference, if positive, between the Conversion
Value and the Initial Principal Amount at Maturity of the Securities surrendered
for conversion (the "Premium") may be satisfied, at the option of the Issuers,
exercisable at any time or from time to time, by an instrument in writing signed
by the Issuers, by delivering to a Converting Holder, in addition to the Cash
Amount, either (i) an amount in cash equal to the Premium or (ii) the number of
whole shares of Common Stock equal to the quotient of (x) the Premium for such
Securities divided by (y) the last reported Sales Price of the Company's Common
Stock on the Conversion Date (if the Conversion Date is not a Business Day, then
on the Business Day immediately preceding the Conversion Date), plus a cash
payment for fractional shares determined pursuant to Section 10.03. At any time
after which the Securities could be converted by action of the Holder, at the
written request of a Holder, the Company will, within five calendar days of
receipt of such request, notify such Holder whether the Premium will be
satisfied in cash or Company Common Stock as aforesaid. Any such notice by the
Company will be irrevocable for 60 calendar days (or such longer period as the
Company may specify on the notice), and then may only be revoked after ten
additional calendar days notice. All elections or notices contemplated to be
given by the Company in this paragraph will be made or given by delivery of
written notice to the Trustee as herein provided and to the Holder.

      In the event that the Issuers elect to satisfy the Premium with Common
Shares, the person in whose name the certificate is registered shall be treated
as a stockholder of record on and after the Conversion Date; provided, however,
that no surrender of a Security on any date when the stock transfer books of the
Company shall be closed shall be effective to constitute the person or persons
entitled to receive the shares of Common Stock upon such conversion as the
record holder or holders of such shares of Common Stock on such date, but such
surrender shall be effective to constitute the person or persons entitled to
receive such shares of Common Stock as the record holder or holders thereof for
all purposes at the close of business on the next succeeding day on which such
stock transfer books are open; such conversion shall be at the Conversion Rate
in effect on the date that such Security shall have been surrendered for
conversion, as if the stock transfer books of the Company had not been closed.

      Upon conversion of a Security, such person shall no longer be a Holder of
such Security.

      No payment or adjustment will be made for dividends on, or other
distributions with respect to, any Common Stock except as provided in this
Article 10. On conversion of a Security, that portion of accrued Contingent
Additional Principal attributable to the period from

                                      -2-
<PAGE>

the Issue Date of the Security through the Conversion Date and (except as
provided below) accrued Contingent Cash Interest with respect to the converted
Security through the Conversion Date shall not be cancelled, extinguished or
forfeited, but rather shall be deemed to be paid in full to the Holder thereof
through delivery of the Cash Amount, together with cash or Common Stock in
respect of the Premium, in exchange for the Security being converted pursuant to
the provisions hereof; and the fair market value of such cash or Common Stock in
respect of the Premium shall be treated as delivered, to the extent thereof,
first in exchange for Contingent Additional Principal accrued through the
Conversion Date and accrued Contingent Cash Interest, and the Cash Amount shall
be treated as delivered in exchange for the Initial Principal Amount at Maturity
of the Security being converted pursuant to the provisions hereof.

      If the Holder converts more than one Security at the same time, the Cash
Amount, together with the cash or Common Stock in respect of the Premium,
issuable upon the conversion shall be based on the total Principal Amount at
Maturity of the Securities converted.

      If the last day on which a Security may be converted is a Legal Holiday,
the Security may be surrendered on the next succeeding day that is not a Legal
Holiday.

      Upon surrender of a Security that is converted in part, the Issuers shall
execute, and the Trustee shall authenticate and deliver to the Holder, a new
Security in an authorized denomination equal in Principal Amount at Maturity to
the unconverted portion of the Security surrendered."

      2.2   Section 10.05 of the Indenture is hereby amended and restated in its
            entirety to read as follows:

            "SECTION 10.05 Company to Provide Stock.

      The Company shall, prior to issuance of any Securities under this Article
10, and from time to time as may be necessary, reserve out of its authorized but
unissued Common Stock a sufficient number of shares of Common Stock to permit
satisfaction of the Premium with Common Stock upon the conversion of the
Securities.

      All shares of Common Stock delivered upon conversion of the Securities
shall be duly authorized, validly issued, fully paid and nonassessable and free
from preemptive rights and any lien or adverse claim.

      The Company will endeavor promptly to comply with all federal and state
securities laws regulating the offer and delivery of shares of Common Stock upon
conversion of Securities, if any, and will list or cause to have quoted such
shares of Common Stock on each national securities exchange or in the
over-the-counter market or such other market on which the Common Stock is then
listed or quoted."

                                      -3-
<PAGE>

      2.3   A new subparagaph (d), to read in its entirety as follows, will be
            added to the existing Section 10.08 of the Indenture:

            SECTION 10.08 Adjustment for Other Distributions.

      "(d) if the Company pays any Regular Cash Dividend during any quarterly
fiscal period for which Contingent Cash Interest is payable, the Conversion Rate
will be adjusted as of the record date for such Regular Cash Dividend based on
the following formula:

                               CR' = CR0 x   SP0
                                          ---------
                                           SP0 - C

      CR0 = the Conversion Rate in effect immediately prior to the record date
            for such Regular Cash Dividend

      CR' = the Conversion Rate in effect immediately after the record date
            for such Regular Cash Dividend; provided that (1) CR' shall not be
            less than 9.09 (except as adjusted pursuant to other provisions of
            this Indenture); and (2) when, if not for clause (1) CR' would be
            less than 9.09, CR0 will be equal to such CR' for purposes of making
            the next quarterly adjustment calculation.

      SP0 = the average of the last reported Sale Prices of the Common Stock
            for the ten consecutive Trading Days prior to the Business Day
            immediately preceding the record date of such Regular Cash Dividend

      C   = the difference of (x) the amount in cash per share paid to holders
            of Common Stock in any quarterly period minus (y) the amount set
            forth for such quarterly fiscal period in Section 5 of the Notes
            divided by 9.09 (appropriately adjusted from time to time for any
            share dividends on, or subdivisions of, the Common Stock)

      Notice of any adjustment to the Conversion Rate as provided in this
Section 10.08(d) need not be given to any Holder unless such adjustment,
together with all prior adjustments pursuant to this Section 10.08(d) for which
notice has not previously been given, would require an increase or decrease of
at least 1% in the Conversion Rate; provided that the Company shall give Holders
annual notice, within 120 days after the end of each fiscal year of the Company
(beginning with the fiscal year ending on December 31, 2007), of all adjustments
made pursuant to this Section 10.08(d) during such fiscal year.

      "Regular Cash Dividends" means quarterly or other periodic cash dividends
on the Company's Common Stock as declared by the Board of Directors as part of
its cash dividend payment practices and that are not designated by the Board of
Directors as extraordinary or special or other nonrecurring dividends."

                                      -4-
<PAGE>

      2.4   Section 10.09 of the Indenture is hereby amended and restated in its
            entirety to read as follows:

            "SECTION 10.09 When Adjustment May Be Deferred.

      "Except for adjustments calculated pursuant to Section 10.08(d), no
adjustment in the Conversion Rate need be made unless the adjustment would
require an increase or decrease of at least 1% in the Conversion Rate. Any
adjustments that are not made shall be carried forward and taken into account in
any subsequent adjustment."

      2.5   Section 5 of Exhibit A-1 to the Indenture is hereby amended and
            restated in its entirety to read as follows:

            "5. Contingent Cash Interest.

      Subject to the record date provisions specified in this paragraph 5, the
Issuers shall pay contingent cash interest ("Contingent Cash Interest") to the
Holder of this Security during any six-month period (each a "Contingent Interest
Period") from August 1 to January 31 or from February 1 to July 31, commencing
on or after August 1, 2007, if the average of the Zero Coupon Zero Yield
Convertible Note Market Prices for each of the days in the Five-Day Period with
respect to such Contingent Interest Period equals or exceeds 120% of the Initial
Principal Amount at Maturity of this Security.

      Contingent Cash Interest, if any, will accrue from the first day of the
applicable six-month period and be payable quarterly on January 31, April 30,
July 31 and October 31 (each a "Contingent Interest Payment Date") of the
relevant six-month period to Holders of the Security on the record date, which
will be each October 15, January 15, April 15 and July 15 immediately preceding
each applicable payment date set forth below.

      For any six-month period, the amount of Contingent Cash Interest payable
on any Contingent Interest Payment Date per $1,000 Initial Principal Amount at
Maturity thereof in respect of any Contingent Interest Period shall equal the
amounts set forth below per $1,000 Initial Principal Amount at Maturity for each
applicable six-month period.

<TABLE>
<CAPTION>
Payment Date                         Quarterly Interest    Payment Date                      Quarterly Interest
<S>                                         <C>            <C>                                      <C>
October 31, 2007...............             $2.11          April 30, 2020.................          $3.51
January 31, 2008...............             $2.11          July 31, 2020..................          $3.51
April 30, 2008.................             $2.11          October 31, 2020...............          $3.63
July 31, 2008..................             $2.11          January 31, 2021...............          $3.63
October 31, 2008...............             $2.22          April 30, 2021.................          $3.63
January 31, 2009...............             $2.22          July 31, 2021..................          $3.63
April 30, 2009.................             $2.22          October 31, 2021...............          $3.75
July 31, 2009..................             $2.22          January 31, 2022...............          $3.75
October 31, 2009...............             $2.34          April 30, 2022.................          $3.75
January 31, 2010...............             $2.34          July 31, 2022..................          $3.75
April 30, 2010.................             $2.34          October 31, 2022...............          $3.86
July 31, 2010..................             $2.34          January 31, 2023...............          $3.86
October 31, 2010...............             $2.46          April 30, 2023.................          $3.86
January 31, 2011...............             $2.46          July 31, 2023..................          $3.86
</TABLE>

                                      -5-
<PAGE>
<TABLE>
<CAPTION>
Payment Date                         Quarterly Interest    Payment Date                      Quarterly Interest
<S>                                         <C>            <C>                                      <C>
April 30, 2011.................             $2.46          October 31, 2023...............          $3.98
July 31, 2011..................             $2.46          January 31, 2024...............          $3.98
October 31, 2011...............             $2.57          April 30, 2024.................          $3.98
January 31, 2012...............             $2.57          July 31, 2024..................          $3.98
April 30, 2012.................             $2.57          October 31, 2024...............          $4.10
July 31, 2012..................             $2.57          January 31, 2025...............          $4.10
October 31, 2012...............             $2.69          April 30, 2025.................          $4.10
January 31, 2013...............             $2.69          July 31, 2025..................          $4.10
April 30, 2013.................             $2.69          October 31, 2025...............          $4.21
July 31, 2013..................             $2.69          January 31, 2026...............          $4.21
October 31, 2013...............             $2.81          April 30, 2026.................          $4.21
January 31, 2014...............             $2.81          July 31, 2026..................          $4.21
April 30, 2014.................             $2.81          October 31, 2026...............          $4.33
July 31, 2014..................             $2.81          January 31, 2027...............          $4.33
October 31, 2014...............             $2.93          April 30, 2027.................          $4.33
January 31, 2015...............             $2.93          July 31, 2027..................          $4.33
April 30, 2015.................             $2.93          October 31, 2027...............          $4.45
July 31, 2015..................             $2.93          January 31, 2028...............          $4.45
October 31, 2015...............             $3.04          April 30, 2028.................          $4.45
January 31, 2016...............             $3.04          July 31, 2028..................          $4.45
April 30, 2016.................             $3.04          October 31, 2028...............          $4.56
July 31, 2016..................             $3.04          January 31, 2029...............          $4.56
October 31, 2016...............             $3.16          April 30, 2029.................          $4.56
January 31, 2017...............             $3.16          July 31, 2029..................          $4.56
April 30, 2017.................             $3.16          October 31, 2029...............          $4.68
July 31, 2017..................             $3.16          January 31, 2030...............          $4.68
October 31, 2017...............             $3.28          April 30, 2030.................          $4.68
January 31, 2018...............             $3.28          July 31, 2030..................          $4.68
April 30, 2018.................             $3.28          October 31, 2030...............          $4.80
July 31, 2018..................             $3.28          January 31, 2031...............          $4.80
October 31, 2018...............             $3.39          April 30, 2031.................          $4.80
January 31, 2019...............             $3.39          July 31, 2031..................          $4.80
April 30, 2019.................             $3.39          October 31, 2031...............          $4.92
July 31, 2019..................             $3.39          January 31, 2032...............          $4.92
October 31, 2019...............             $3.51          April 30, 2032.................          $4.92
January 31, 2020...............             $3.51          July 31, 2032..................          $4.92
</TABLE>

      "Five-Day Period" means, with respect to any Contingent Interest Period,
the five trading days ending on the second trading day immediately preceding the
first day of such Contingent Interest Period; provided, however, that if the
Company shall have declared a Regular Cash Dividend on its Common Stock that is
payable during such Contingent Interest Period but for which the record date for
determining stockholders entitled thereto precedes the first day of such
Contingent Interest Period, then "Five-Day Period" shall mean, with respect to
such Contingent Interest Period, the five trading days ending on the second
trading day immediately preceding such record date.

      "Regular Cash Dividends" means quarterly or other periodic cash dividends
on the Company's Common Stock as declared by the Board of Directors as part of
its cash dividend payment practices and that are not designated by the Board of
Directors as extraordinary or special or other nonrecurring dividends.

      "Zero Coupon Zero Yield Convertible Note Market Price" means, as of any
date of determination, the average of the secondary market bid quotations per
$1,000 Principal

                                      -6-
<PAGE>

Amount at Maturity obtained by the Bid Solicitation Agent for $10 million
Principal Amount at Maturity of Securities at approximately 4:00 p.m., New York
City time, on such determination date from three independent nationally
recognized securities dealers in The City of New York (none of which shall be an
Affiliate of the Issuers) selected by the Issuers; provided, however, if (a) at
least three such bids are not obtained by the Bid Solicitation Agent or (b) in
the Issuers' reasonable judgment, the bid quotations are not indicative of the
secondary market value of the Securities as of such determination date, then the
Zero Coupon Zero Yield Convertible Note Market Price for such determination date
shall equal (i) the Conversion Rate in effect as of such determination date
multiplied by (ii) the average of the Sale Prices of the Common Stock for each
of the five trading days ending on such determination date, appropriately
adjusted to take into account the occurrence, during the period commencing on
the first of such trading days during such five trading day period and ending on
such determination date, of any event described in Section 10.06, 10.07 or 10.08
(subject to the conditions set forth in Sections 10.09 and 10.10) of the
Indenture.

      The Issuers will determine every six months, commencing August 1, 2007,
whether the conditions to the payment of Contingent Cash Interest have been
satisfied and, if so, the Issuers shall promptly notify the Holders of this
Security of such determination and shall use their reasonable best efforts to
post this information on their web site or, at their option, otherwise publicly
disclose this information."

      2.6   Section 9 of Exhibit A-1 to the Indenture is hereby amended and
            restated in its entirety to read as follows:

"9. Conversion.

      Holders may surrender Securities for conversion only if at least one of
the conditions described in (a) through (d) below is satisfied. In addition, a
Security for which a Holder has delivered a Purchase Notice or a Change in
Control Purchase Notice requiring the Issuers to purchase the Security may be
surrendered for conversion only if such notice is withdrawn in accordance with
the Indenture.

      The initial Conversion Rate is 9.09 shares per $1,000 Initial Principal
Amount at Maturity of a Security, subject to adjustment upon the occurrence of
certain events described in the Indenture. A Holder otherwise entitled to a
fractional share will receive cash in an amount equal to the value of such
fractional share based on the Sale Price on the trading day immediately
preceding the Conversion Date.

      The ability to surrender Securities for conversion will expire at the
close of business on July 31, 2032.

      (a) Before July 31, 2022, Holders may surrender a Security for conversion
at the then-applicable conversion price during any calendar quarter, commencing
after March 31, 2002 if the average Conversion Values of the Security for each
of the last 20 trading days in the preceding calendar quarter is greater than or
equal to a specified percentage of the Initial Principal Amount at Maturity;
125% for the quarter ending June 30, 2002, and increasing 5% per quarter for
each quarter thereafter up to a maximum of 220% of the Initial Principal Amount
at

                                      -7-
<PAGE>

Maturity of the Security for the quarter ending June 30, 2007. Thereafter, this
percentage shall remain at 220%. If the foregoing condition is satisfied at any
time after July 31, 2003 and before July 31, 2022, then the Securities will
become and remain convertible at any time thereafter at the option of the
Holder, through maturity. On or after July 31, 2022, Holders may surrender a
Security for conversion during any calendar quarter if the average of the
Conversion Values of the Security for each of the last 20 trading days in the
preceding calendar quarter is greater than or equal to 110% of the Principal
Amount at Maturity of the Security. If the foregoing condition is satisfied,
then the Securities will become and remain convertible at any time thereafter at
the option of the Holder, through maturity.

      (b) Holders may also surrender a Security for conversion at the
then-applicable conversion price at any time after the credit rating assigned to
the Securities is reduced to Baa3 or lower by Moody's Investors Service, Inc. or
BBB or lower by Standard & Poor's Ratings Services, even if the credit rating
assigned has subsequently been changed to a higher rating.

      (c) A Holder may surrender for conversion at the then-applicable
conversion price a Security with respect to which the Issuers have mailed a
Redemption Notice at any time prior to the close of business on the second
Business Day prior to the Redemption Date, even if it is not otherwise
convertible at that time.

      (d) If the Company elects to

   o  distribute to all Holders of Common Stock certain rights entitling them to
      purchase, for a period expiring within 60 days, Common Stock at less than
      the Sale Price at the time, or

   o  distribute to all Holders of Common Stock assets, debt securities or
      certain rights to purchase securities of the Company, which distribution
      has a per share value as determined by the Company's Board of Directors
      exceeding 15% of the closing price of the Common Stock on the day
      preceding the declaration date for such distribution,

the Company must notify the Holders of Securities at least 20 days prior to the
Ex-Dividend Date for such distribution. Once the Company has given such notice,
Holders may surrender their Securities for conversion at the then-applicable
conversion price at any time thereafter until the earlier of the close of
business on the Business Day prior to the Ex-Dividend Date or the Company's
announcement that such distribution will not take place.

      Contingent Cash Interest will not be paid on Securities that are
converted; provided, however that Holders of Securities surrendered for
conversion during the period from the close of business on any record date for
determining an obligation to pay Contingent Cash Interest to the opening of
business on the date on which such Contingent Cash Interest is payable, shall be
entitled to receive such Contingent Cash Interest on the date on which such
Contingent Cash Interest is payable. Except Securities with respect to which the
Issuers have mailed a Notice of Redemption, Securities surrendered for
conversion during such periods must be accompanied by

                                      -8-
<PAGE>

payment of an amount equal to the Contingent Cash Interest with respect thereto
that the registered Holder is to receive.

      The Conversion Rate will not be adjusted for accrued Contingent Additional
Principal, if any, or Contingent Cash Interest, if any. As soon as practicable
following the Conversion Date, the Issuers will deliver through the Conversion
Agent, the Cash Amount, together with cash or a certificate for the number of
full shares of Common Stock into which the Premium of any Security is converted,
together with and any cash payment for fractional shares. Delivery to the Holder
of the Cash Amount, together with such cash or shares of Common Stock
deliverable in connection with the Premium, will be deemed to satisfy the
Issuers' obligation to pay the Principal Amount at Maturity of and any accrued
Contingent Additional Principal on the Security.

      Subject to the provisions of this paragraph 9 and notwithstanding the fact
that any other condition to conversion has not been satisfied, in the event the
Company is a party to a consolidation, merger or binding share exchange pursuant
to which the Common Stock would be converted into cash, securities or other
property as set forth in Section 10.14 of the Indenture, the Securities may be
surrendered for conversion at any time from and after the date which is 15 days
prior to the date the Company announces the anticipated effective time until 15
days after the actual effective date of such transaction, and at the effective
time of such transaction the right to convert a Security into Common Stock will
be deemed to have changed into a right to convert it into the kind and amount of
cash, securities or other property which the Holder would have received if the
Holder had converted its Security immediately prior to the transaction. If the
transaction also constitutes a Change in Control, the Holder will be able to
require the Company to purchase all or a portion of its Securities as described
under paragraph 7 herein.

      To convert a Security, a Holder must (1) complete and manually sign the
conversion notice below (or complete and manually sign a facsimile of such
notice) and deliver such notice to the Conversion Agent, (2) surrender the
Security to the Conversion Agent, (3) furnish appropriate endorsements and
transfer documents if required by the Conversion Agent, the Issuers or the
Trustee and (4) pay any transfer or similar tax, if required. The "Conversion
Date" as used herein refers to the date on which all of the foregoing
requirements have been satisfied.

      A Holder may convert a portion of a Security if the Initial Principal
Amount at Maturity of such portion is $1,000 or an integral multiple of $1,000.
No payment or adjustment will be made for dividends on the Common Stock except
as provided in the Indenture. On conversion of a Security, that portion of
accrued Contingent Additional Principal attributable to the period from the
Issue Date through the Conversion Date and (except as provided above) accrued
Contingent Cash Interest with respect to the converted Security shall not be
cancelled, extinguished or forfeited, but rather shall be deemed to be paid in
full to the Holder thereof through the delivery of the Cash Amount, together
with cash or Common Stock in respect of the Premium, in exchange for the
Security being converted pursuant to the terms hereof; and the fair market value
of such cash or Common Stock in respect of the Premium, shall be treated as
delivered to the extent thereof, first in exchange for Contingent Additional
Principal accrued through the Conversion Date and accrued Contingent Cash
Interest, and the Cash Amount shall be treated as delivered in exchange for the
Initial Principal Amount at Maturity of the Security being converted pursuant to
the provisions hereof.

                                      -9-
<PAGE>

      The Conversion Rate will be adjusted as provided in Article 10 of the
Indenture. However, no adjustment need be made if Securityholders may
participate in the transaction or in certain other cases. The Company from time
to time may voluntarily increase the Conversion Rate.

      In certain circumstances as provided for in the Indenture, when a Holder
surrenders a Security for conversion, the Conversion Agent may first offer the
Security to a financial institution chosen by the Issuers who will have the
option, but not the obligation (unless separately agreed to by it and the
Issuers at the time) to agree to exchange those Securities for the number of
shares of Common Stock that the Holder of those Securities would have been
otherwise entitled to receive upon conversion, plus cash for any fractional
shares."

3.    Separability Clause. In case any provision in this Supplemental Indenture
      shall be invalid, illegal or unenforceable, the validity, legality and
      enforceability of the remaining provisions shall not in any way be
      affected or impaired thereby.

4.    Modification, Amendment and Waiver. The provisions of this Supplemental
      Indenture may not be amended, supplemented, modified or waived except by a
      execution of a Supplemental Indenture executed by the Issuers, the Company
      and, to the extent such amendment, supplement or waiver limits or impairs
      the rights of any Securityholder, by such Securityholder. Any such
      amendment shall comply with Article 9 of the Indenture. Until an
      amendment, waiver or other action by Securityholders becomes effective, a
      consent thereto by a Securityholder of a Security hereunder is a
      continuing consent by the Securityholder and every subsequent
      Securityholder of that Security or portion of the Security that evidences
      the same obligation as the consenting Securityholder's Security, even if
      notation of the consent, waiver or action is not made on the Security.
      However, any such Securityholder or subsequent Securityholder may revoke
      the consent, waiver or action as to such Securityholder's Security or
      portion of the Security if the Trustee receives the notice of revocation
      before the date the amendment, waiver or action becomes effective. After
      an amendment, waiver or action becomes effective, it shall bind every
      Securityholder.

5.    Ratification of Indenture; Supplemental Indenture Part of Indenture.
      Except as expressly amended hereby, the Indenture is in all respects
      ratified and confirmed and all the terms, conditions and provisions
      thereof shall remain in full force and effect. In the event of a conflict
      between the terms and conditions of the Indenture and the terms and
      conditions of this Supplemental Indenture, then the terms and conditions
      of this Supplemental Indenture shall prevail. This Supplemental Indenture
      shall form a part of the Indenture for all purposes, and every holder of
      Securities heretofore or hereafter authenticated and delivered shall be
      bound hereby.

6.    Trust Indenture Acts Controls. If any provision of this Supplemental
      Indenture limits, qualifies or conflicts with any provision of the Trust
      Indenture Act of 1939, as amended ("TIA"), that is required under the TIA
      to be part of and govern any provision of this Supplemental Indenture, the
      provision of the TIA shall control. If any provision of this Supplemental
      Indenture modifies or excludes any provisions of the TIA that may be so
      modified or excluded, the provisions of the TIA shall be deemed to apply
      to the

                                      -10-
<PAGE>

      Indenture as so modified or to be excluded by this Supplemental Indenture,
      as the case may be.

7.    Governing Law. THIS SUPPLEMENTAL INDENTURE SHALL BE GOVERNED BY AND
      CONSTRUED IN ACCORDANCE WITH THE LAWS OF THE STATE OF NEW YORK, AS APPLIED
      TO CONTRACTS MADE AND PERFORMED WITHIN THE STATE OF NEW YORK WITHOUT
      GIVING EFFECT TO THE PRINCIPLES OF CONFLICTS OF LAW.

8.    Trustee Makes No Representation. The statements herein are deemed to be
      those of the Company, OCI or OFI, as applicable. The Trustee makes no
      representation as to the validity or sufficiency of this Supplemental
      Indenture.

9.    Multiple Originals. The parties may sign any number of copies of this
      Supplemental Indenture. Each signed copy shall be an original, but all of
      them together represent the same agreement. One signed copy is enough to
      prove this Supplemental Indenture.

10.   Effect of Headings. The Section headings herein are for convenience only
      and shall not effect the construction thereof.

11.   Notices. Any request, demand, authorization, notice, waiver, consent or
      communication to any of the parties shall be made as set forth in Section
      12.02 of the Indenture, as said Section may be amended hereby.

12.   Successors. All agreements of each of the Company, OCI and OFI in respect
      of this Supplemental Indenture shall bind its successor.

                            [Signature page follows]

                                      -11-
<PAGE>

         IN WITNESS WHEREOF, this Supplemental Indenture has been duly executed
by the Company, OCI and the Trustee as of the date first written above.

                                        OMNICOM GROUP INC.

                                        By: /s/ Randall J. Weisenburger
                                            -----------------------------------
                                            Name:  Randall J. Weisenburger
                                            Title: Executive Vice President
                                                   and Chief Financial Officer

                                        OMNICOM CAPITAL INC.

                                        By: /s/ Dennis E. Hewitt
                                            -----------------------------------
                                            Name:  Dennis E. Hewitt
                                            Title: Chief Executive Officer

                                        OMNICOM FINANCE INC.

                                        By: /s/ Randall J. Weisenburger
                                            -----------------------------------
                                            Name:  Randall J. Weisenburger
                                            Title: Chief Executive Officer

                                        JPMORGAN CHASE BANK, as Trustee

                                        By: /s/ William G. Keenan
                                            -----------------------------------
                                            Name:  William G. Keenan
                                            Title: Vice President

                                      -12-Exhibit 4.2

                                                               Execution Version

                          SECOND SUPPLEMENTAL INDENTURE

      This SECOND SUPPLEMENTAL INDENTURE (the "Supplemental Indenture") dated as
of November 4, 2004 among OMNICOM GROUP INC., a New York corporation (the
"Company"), OMNICOM CAPITAL INC., a Connecticut corporation ("OCI"), OMNICOM
FINANCE INC., a Delaware corporation ("OFI" and together with the Company and
OCI, the "Issuers"), and JPMORGAN CHASE BANK, as trustee under the indenture
referred to below (the "Trustee").

                              W I T N E S S E T H:

      WHEREAS, the Issuers and the Trustee have heretofore executed and
delivered to the Trustee an Indenture dated February 7, 2001, as amended by the
First Supplemental Indenture, dated February 13, 2004 (as so amended, the
"Indenture"), providing for the issuance of an aggregate principal amount of up
to $850,000,000 of Liquid Yield Option(TM) Notes due 2031 (the "Securities"),
all of which have been issued and $847,031,000 of which are outstanding on the
date hereof;

      WHEREAS, the Issuers desire to surrender their right under Section 3.08(b)
of the Indenture to elect to pay for Securities being purchased by the Issuers
pursuant to Section 3.08(a) of the Indenture with Common Stock;

      WHEREAS, it is in the best interests of the Issuers to surrender such
right;

      WHEREAS, Section 9.01(6) of the Indenture provides that the Issuers and
the Trustee may amend or supplement the Indenture without the consent of any
Securityholder to surrender any right, power or option conferred by this
Indenture on the Issuers;

      WHEREAS, an Opinion of Counsel and an Officer's Certificate have been
delivered to the Trustee under Section 9.06; and

      WHEREAS, pursuant to Sections 9.01 and 9.06 of the Indenture, the Trustee
and the Issuers are authorized to execute and deliver this Supplemental
Indenture;

      NOW THEREFORE, for good and valuable consideration, the receipt of which
is hereby acknowledged, the Issuers and the Trustee mutually covenant and agree
for the equal and ratable benefit of the holders of the Securities as follows:

      1. Definitions. All capitalized terms used but not defined herein shall
have the meanings given to such terms in the Indenture.

      2. Amendments. The Indenture be and hereby is amended as follows:

      2.1 Section 1.01 and Section 1.02 of the Indenture are hereby amended so
that the cross-references to the following definitions contained in Section 1.02
are deleted from Section 1.02 and such definitions are inserted in Section 1.01
in their proper alphabetical order as follows:

<PAGE>

      "cash" means U.S. legal tender;

      "Exchange Act" means the Securities Exchange Act of 1934, as amended; and

      "Securities Act" means the Securities Act of 1933, as amended.

      2.2 Section 1.02 of the Indenture is hereby amended so that the following
definitions are inserted in Section 1.02 in their proper alphabetical order as
follows:

            "Issuers' Notice" ..........3.08(c); and

            "Issuers' Notice Date" ....3.08(b).

      2.3 Section 1.02 and Section 12.08 of the Indenture are hereby amended so
that the reference to the defined terms "Company Notice," "Company Notice Date"
and "Market Price" are deleted from the aforementioned sections.

      2.4 Section 3.08 of the Indenture is hereby amended and restated in its
entirety to read as follows:

            "SECTION 3.08 Purchase of Securities at Option of the Holder. (a)
General. If a Holder exercises its right to require the Issuers to purchase
Securities pursuant to paragraph 7 of the Securities, such Securities shall be
purchased by the Issuers pursuant to paragraph 7 of the Securities on each
February 7 from February 7, 2002 through February 7, 2030 (each February 7 in
the aforementioned period, a "Purchase Date"), at a purchase price equal to (i)
the Issue Price of the Security for any Purchase Date occurring on or prior to
February 7, 2021 and (ii) the Issue Price plus accrued Contingent Additional
Principal, if any, as of the relevant Purchase Date for any Purchase Date
occurring after February 7, 2021, at the option of the Holder thereof, upon:

            (1) delivery to the Paying Agent, by the Holder of a written notice
      of purchase (a "Purchase Notice") at any time from the opening of business
      on the date that is at least 20 Business Days prior to a Purchase Date
      until the close of the third Business Day prior to such Purchase Date
      stating:

                  (A) the certificate number of the Security which the Holder
            will deliver to be purchased,

                  (B) the portion of the Principal Amount at Maturity of the
            Security which the Holder will deliver to be purchased, which
            portion must be a Principal Amount at Maturity of $1,000 or an
            integral multiple thereof, and

                  (C) that such Security shall be purchased as of the Purchase
            Date pursuant to the terms and conditions specified in paragraph 7
            of the Securities and in this Indenture; and

            (2) delivery of such Security to the Paying Agent prior to, on or
      after the Purchase Date (together with all necessary endorsements) at the
      offices of the Paying Agent, such delivery being a condition to receipt by
      the Holder of the Purchase Price

                                      -2-
<PAGE>

      therefor; provided, however, that such Purchase Price shall be so paid
      pursuant to this Section 3.08 only if the Security so delivered to the
      Paying Agent shall conform in all respects to the description thereof in
      the related Purchase Notice, as determined by the Issuers.

            The Issuers shall purchase from the Holder thereof, pursuant to this
Section 3.08, a portion of a Security if the Principal Amount at Maturity of
such portion is $1,000 or an integral multiple of $1,000. Provisions of this
Indenture that apply to the purchase of all of a Security also apply to the
purchase of such portion of such Security.

            Any purchase by the Issuers contemplated pursuant to the provisions
of this Section 3.08 shall be consummated by the delivery of the cash
consideration to be received by the Holder (including accrued and unpaid
Contingent Cash Interest, if any) promptly following the later of the Purchase
Date and the time of delivery of the Security.

            Notwithstanding anything herein to the contrary, any Holder
delivering to the Paying Agent the Purchase Notice contemplated by this Section
3.08(a) shall have the right to withdraw such Purchase Notice at any time prior
to the close of business on the Business Day prior to the Purchase Date by
delivery of a written notice of withdrawal to the Paying Agent in accordance
with Section 3.10.

            The Paying Agent shall promptly notify the Issuers of the receipt by
it of any Purchase Notice or written notice of withdrawal thereof.

            (b) Purchase with Cash. On each Purchase Date, the Purchase Price of
Securities in respect of which a Purchase Notice pursuant to Section 3.08(a) has
been given shall be paid by the Issuers with cash equal to the aggregate
Purchase Price of such Securities.

            (c) The Issuers' Notice. The Issuers shall send a notice (the
"Issuers' Notice") to the Holders (and to beneficial owners as required by
applicable law) in the manner provided in Section 12.02 not less than 20
Business Days prior to the applicable Purchase Date (the "Issuers' Notice
Date"). Each Issuers Notice shall include a form of Purchase Notice to be
completed by a Securityholder and shall state:

            (i) the Purchase Price, the Conversion Rate and, to the extent known
      at the time of such notice, the amount of Contingent Cash Interest, if
      any, that will be accrued and payable with respect to the Securities as of
      the Purchase Date;

            (ii) the name and address of the Paying Agent and the Conversion
      Agent;

            (iii) that Securities as to which a Purchase Notice has been given
      may be converted pursuant to Article 10 hereof only if the applicable
      Purchase Notice has been withdrawn in accordance with the terms of this
      Indenture;

            (iv) that Securities must be surrendered to the Paying Agent to
      collect payment of the Purchase Price and Contingent Cash Interest, if
      any;

                                      -3-
<PAGE>

           (v) that the Purchase Price for any Security as to which a Purchase
      Notice has been given and not withdrawn, together with any accrued
      Contingent Cash Interest payable with respect thereto, will be paid
      promptly following the later of the Purchase Date and the time of
      surrender of such Security as described in (iv);

            (vi) the procedures the Holder must follow to exercise rights under
      Section 3.08 and a brief description of those rights;

            (vii) briefly, the conversion rights of the Securities;

            (viii) the procedures for withdrawing a Purchase Notice (including,
      without limitation, for a conditional withdrawal pursuant to the terms of
      Section 3.10);

            (ix) that, unless the Issuers default in making payment of such
      Purchase Price, Contingent Additional Principal and Contingent Cash
      Interest, if any, on Securities called for redemption will cease to accrue
      on after the Purchase Date; and

            (x) the CUSIP number of the Securities.

                        At the Issuers' request, the Trustee shall give such
            Issuers' Notice in the Issuers' name and at the Issuers' expense;
            provided, however, that, in all cases, the text of such Issuers'
            Notice shall be prepared by the Issuers.

            (d) Procedure upon Purchase. The Issuers shall deposit cash at the
time and in the manner as provided in Section 3.11, sufficient to pay the
aggregate Purchase Price of, and any accrued and unpaid Contingent Cash Interest
with respect to, all Securities to be purchased pursuant to this Section 3.08."

      2.5 Section 3.10 of the Indenture is hereby amended and restated in its
entirety to read as follows:

            "SECTION 3.10 Effect of Purchase Notice or Change in Control
Purchase Notice. Upon receipt by the Paying Agent of the Purchase Notice or
Change in Control Purchase Notice specified in Section 3.08(a) or Section
3.09(c), as applicable, the Holder of the Security in respect of which such
Purchase Notice or Change in Control Purchase Notice, as the case may be, was
given shall (unless such Purchase Notice or Change in Control Purchase Notice is
withdrawn as specified in the following two paragraphs) thereafter be entitled
to receive solely the Purchase Price or Change in Control Purchase Price, as the
case may be, and any accrued and unpaid Contingent Cash Interest, with respect
to such Security. Such Purchase Price or Change in Control Purchase Price and
Contingent Cash Interest, if any, shall be paid to such Holder, subject to
receipts of funds and/or securities by the Paying Agent, promptly following the
later of (x) the Purchase Date or the Change in Control Purchase Date, as the
case may be, with respect to such Security (provided the conditions in Section
3.08(a) or Section 3.09(c), as applicable, have been satisfied) and (y) the time
of delivery of such Security to the Paying Agent by the Holder thereof in the
manner required by Section 3.08(a) or Section 3.09(c), as applicable. Securities
in respect of which a Purchase Notice or Change in Control Purchase Notice, as
the case may be, has been given by the Holder thereof may not be converted
pursuant to Article 10 hereof on or after the date of the delivery of such
Purchase Notice or Change in Control Purchase Notice, as the case may be, unless
such Purchase Notice or Change in Control Purchase

                                      -4-
<PAGE>

Notice, as the case may be, has first been validly withdrawn as specified in the
following two paragraphs.

            A Purchase Notice or Change in Control Purchase Notice, as the case
may be, may be withdrawn by means of a written notice of withdrawal delivered to
the office of the Paying Agent in accordance with the Purchase Notice or Change
in Control Purchase Notice, as the case may be, at any time prior to the close
of business on the Purchase Date or the Change in Control Purchase Date, as the
case may be, specifying:

            (1) the certificate number of the Security in respect of which such
      notice of withdrawal is being submitted,

            (2) the Principal Amount at Maturity of the Security with respect to
      which such notice of withdrawal is being submitted, and

            (3) the Principal Amount at Maturity, if any, of such Security which
      remains subject to the original Purchase Notice or Change in Control
      Purchase Notice, as the case may be, and which has been or will be
      delivered for purchase by the Issuers.

            There shall be no purchase of any Securities pursuant to Section
3.08 or 3.09 if there has occurred (prior to, on or after, as the case may be,
the giving, by the Holders of such Securities, of the required Purchase Notice
or Change in Control Purchase Notice, as the case may be) and is continuing an
Event of Default (other than a default in the payment of the Purchase Price or
Change in Control Purchase Price, as the case may be, and any accrued and unpaid
Contingent Cash Interest with respect to such Securities). The Paying Agent will
promptly return to the respective Holders thereof any Securities (x) with
respect to which a Purchase Notice or Change in Control Purchase Notice, as the
case may be, has been withdrawn in compliance with this Indenture, or (y) held
by it during the continuance of an Event of Default (other than a default in the
payment of the Purchase Price or Change in Control Purchase Price, as the case
may be, and any accrued and unpaid Contingent Cash Interest with respect to such
Securities) in which case, upon such return, the Purchase Notice or Change in
Control Purchase Notice with respect thereto shall be deemed to have been
withdrawn."

      2.6 The second paragraph of Section 7 of Exhibit A-1 to the Indenture is
hereby amended and restated in its entirety to read as follows:

            "The Purchase Price shall be paid in cash."

      3. Separability Clause. In case any provision in this Supplemental
Indenture shall be invalid, illegal or unenforceable, the validity, legality and
enforceability of the remaining provisions shall not in any way be affected or
impaired thereby.

      4. Modification, Amendment and Waiver. The provisions of this Supplemental
Indenture may not be amended, supplemented, modified or waived except by a
execution of a Supplemental Indenture executed by the Issuers, and, to the
extent such amendment, supplement or waiver limits or impairs the rights of any
Securityholder, by such Securityholder. Any such amendment shall comply with
Article 9 of the Indenture. Until an amendment, waiver or other

                                      -5-
<PAGE>

action by Securityholders becomes effective, a consent thereto by a
Securityholder of a Security hereunder is a continuing consent by the
Securityholder and every subsequent Securityholder of that Security or portion
of the Security that evidences the same obligation as the consenting
Securityholder's Security, even if notation of the consent, waiver or action is
not made on the Security. However, any such Securityholder or subsequent
Securityholder may revoke the consent, waiver or action as to such
Securityholder's Security or portion of the Security if the Trustee receives the
notice of revocation before the date the amendment, waiver or action becomes
effective. After an amendment, waiver or action becomes effective, it shall bind
every Securityholder.

      5. Ratification of Indenture; Supplemental Indenture Part of Indenture.
Except as expressly amended hereby, the Indenture is in all respects ratified
and confirmed and all the terms, conditions and provisions thereof shall remain
in full force and effect. In the event of a conflict between the terms and
conditions of the Indenture and the terms and conditions of this Supplemental
Indenture, then the terms and conditions of this Supplemental Indenture shall
prevail. This Supplemental Indenture shall form a part of the Indenture for all
purposes, and every holder of Securities heretofore or hereafter authenticated
and delivered shall be bound hereby.

      6. Trust Indenture Acts Controls. If any provision of this Supplemental
Indenture limits, qualifies or conflicts with any provision of the Trust
Indenture Act of 1939, as amended ("TIA"), that is required under the TIA to be
part of and govern any provision of this Supplemental Indenture, the provision
of the TIA shall control. If any provision of this Supplemental Indenture
modifies or excludes any provisions of the TIA that may be so modified or
excluded, the provisions of the TIA shall be deemed to apply to the Indenture as
so modified or to be excluded by this Supplemental Indenture, as the case may
be.

      7. Governing Law. THIS SUPPLEMENTAL INDENTURE SHALL BE GOVERNED BY AND
CONSTRUED IN ACCORDANCE WITH THE LAWS OF THE STATE OF NEW YORK, AS APPLIED TO
CONTRACTS MADE AND PERFORMED WITHIN THE STATE OF NEW YORK WITHOUT GIVING EFFECT
TO THE PRINCIPLES OF CONFLICTS OF LAW.

      8. Trustee Makes No Representation. The statements herein are deemed to be
those of the Company, OCI or OFI, as applicable. The Trustee makes no
representation as to the validity or sufficiency of this Supplemental Indenture.

      9. Multiple Originals. The parties may sign any number of copies of this
Supplemental Indenture. Each signed copy shall be an original, but all of them
together represent the same agreement. One signed copy is enough to prove this
Supplemental Indenture.

      10. Effect of Headings. The Section headings herein are for convenience
only and shall not effect the construction thereof.

      11. Notices. Any request, demand, authorization, notice, waiver, consent
or communication to any of the parties shall be made as set forth in Section
12.02 of the Indenture, as said Section may be amended hereby.

                                      -6-
<PAGE>

      12. Successors. All agreements of each of the Company, OCI and OFI in
respect of this Supplemental Indenture shall bind its successor.

                            [Signature page follows]

                                      -7-
<PAGE>

      IN WITNESS WHEREOF, this Supplemental Indenture has been duly executed by
the Company, OCI, OFI and the Trustee as of the date first written above.

                                       OMNICOM GROUP INC.

                                       By:    /s/ Randall J. Weisenburger
                                              ----------------------------------
                                       Name:  Randall J. Weisenburger
                                       Title: Executive Vice President and Chief
                                              Financial Officer

                                       OMNICOM CAPITAL INC.

                                       By:    /s/ Michael J. O'Brien
                                              ----------------------------------
                                       Name:  Michael J. O'Brien
                                       Title: Secretary

                                       OMNICOM FINANCE INC.

                                       By: /s/ Randall J. Weisenburger
                                              ----------------------------------
                                       Name:  Randall J. Weisenburger
                                       Title: Chief Executive Officer

                                       JPMORGAN CHASE BANK, as Trustee

                                       By:  /s/ Carol Ng
                                              ----------------------------------
                                       Name:  Carol Ng
                                       Title: Vice President

                                      -8-

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