<PAGE>

   As filed with the Securities and Exchange Commission on January 12, 2000
                                                 Registration No. 333- _________

                      SECURITIES AND EXCHANGE COMMISSION
                            Washington, D.C.  20549

                                   FORM S-8

                         REGISTRATION STATEMENT UNDER
                          THE SECURITIES ACT OF 1933

                                  CMGI, INC.
            (Exact Name of Registrant as Specified in Its Charter)

               DELAWARE                                        04-2921333
     (State or Other Jurisdiction of                        (I.R.S. Employer
     Incorporation or Organization)                       Identification Number)

     100 BRICKSTONE SQUARE, ANDOVER, MASSACHUSETTS               01810
       (Address of Principal Executive Offices)               (Zip Code)

                         ADFORCE, INC. 1997 STOCK PLAN
            ADFORCE, INC. STARPOINT SOFTWARE, INC. 1996 STOCK PLAN
                   ADFORCE, INC. 1999 EQUITY INCENTIVE PLAN
                ADFORCE, INC. 1999 EMPLOYEE STOCK PURCHASE PLAN
                ADFORCE, INC. 1999 DIRECTORS STOCK OPTION PLAN
                ADFORCE, INC. INCENTIVE STOCK OPTION AGREEMENTS

                           (Full Title of the Plan)

                              DAVID S. WETHERELL
                     PRESIDENT AND CHIEF EXECUTIVE OFFICER
                                  CMGI, INC.
                             100 BRICKSTONE SQUARE
                         Andover, Massachusetts  01810
                    (Name and Address of Agent for Service)

                                 (978) 684-3600
         (Telephone Number, Including Area Code, of Agent for Service)

                                   Copies to:

                           WILLIAM WILLIAMS II, ESQ.
                       VICE PRESIDENT AND GENERAL COUNSEL
                                   CMGI, INC.
                             100 BRICKSTONE SQUARE
                         Andover, Massachusetts  01810

                        CALCULATION OF REGISTRATION FEE



<TABLE>
<CAPTION>
                                          Proposed Maximum       Proposed Maximum
       Title of             Amount            Offering          Aggregate Offering        Amount of
      Securities            to be               Price                 Price             Registration
        to be             Registered          Per Share                                      Fee
      Registered
----------------------  -------------     ----------------      ------------------      ------------
<S>                     <C>             <C>                    <C>                   <C>

Common Stock, $.01        1,972,488            $129.67(1)           $255,772,519(1)       $67,524
 par value                  shares
--------------------------------------------------------------------------------------------------------
</TABLE>

(1)  Estimated solely for the purpose of calculating the registration fee, and
     based on the average of the high and low prices of the Common Stock on the
     Nasdaq National Market on January 7, 2000 in accordance with Rules 457(c)
     and 457(h) under the Securities Act of 1933.


<PAGE>

PART I.  INFORMATION REQUIRED IN THE SECTION 10(a) PROSPECTUS

          The information required by Part I is included in documents sent or
given to participants in the Registrant's AdForce, Inc. 1997 Stock Plan,
AdForce, Inc. Starpoint Software, Inc. 1996 Stock Plan, AdForce, Inc. 1999
Equity Incentive Plan, AdForce, Inc.1999 Employee Stock Purchase Plan, AdForce,
Inc. 1999 Directors Stock Option Plan and AdForce, Inc. Incentive Stock Option
Agreements, pursuant to Rule 428(b)(1) of the Securities Act of 1933, as
amended (the "Securities Act").

PART II.  INFORMATION REQUIRED IN THE REGISTRATION STATEMENT

     Item 3.  Incorporation of Documents by Reference
              ---------------------------------------

          The Registrant is subject to the informational and reporting
requirements of Sections 13(a), 14 and 15(d) of the Securities Exchange Act of
1934, as amended (the "Exchange Act"), and in accordance therewith files
reports, proxy statements and other information with the Securities and Exchange
Commission (the "Commission").  The following documents, which are on file with
the Commission, are incorporated in this Registration Statement by reference:

          (1)  The Registrant's latest annual report filed pursuant to Section
               13(a) or 15(d) of the Exchange Act, or the latest prospectus
               filed pursuant to Rule 424(b) under the Securities Act that
               contains audited financial statements for the Registrant's latest
               fiscal year for which such statements have been filed.

          (2)  All other reports filed pursuant to Section 13(a) or 15(d) of the
               Exchange Act since the end of the fiscal year covered by the
               document referred to in (1) above.

          (3)  The description of the common stock of the Registrant, $.01 par
               value per share (the "Common Stock"), contained in a registration
               statement filed under the Exchange Act, including any amendment
               or report filed for the purpose of updating such description.

          All documents subsequently filed by the Registrant pursuant to
Sections 13(a), 13(c), 14 and 15(d) of the Exchange Act, prior to the filing of
a post-effective amendment which indicates that all shares of Common Stock
offered hereby have been sold or which deregisters all shares of Common Stock
then remaining unsold, shall be deemed to be incorporated by reference herein
and to be part hereof from the date of the filing of such documents.  Any
statement contained in a document incorporated or deemed to be incorporated by
reference herein shall be deemed to be modified or superseded for purposes of
this Registration Statement to the extent that a statement contained herein or
in any other subsequently filed document which also is or is deemed to be
incorporated by reference herein modifies or supersedes such statement.  Any
statement so modified or superseded shall not be deemed, except as so modified
or superseded, to constitute a part of this Registration Statement.

     Item 4.  Description of Securities
              -------------------------

          Not applicable.

     Item 5.  Interests of Named Experts and Counsel
              --------------------------------------

          The legality of the Common Stock being offered hereby will be passed
for the Registrant by Hale and Dorr LLP, Boston, Massachusetts. Certain partners
of Hale and Dorr LLP and their affiliates beneficially own an aggregate of 3,150
shares of Common Stock of the Registrant.
<PAGE>

          Item 6.  Indemnification of Directors and Officers
                   -----------------------------------------

          Section 145 of the Delaware General Corporation Law grants the
Registrant the power to indemnify each person who was or is a party or is
threatened to be made a party to any threatened, pending or completed action,
suit, or proceeding, whether civil, criminal, administrative, or investigative
by reason of the fact that he is or was a director, officer, employee or agent
of the Registrant, or is or was serving at the request of the Registrant as a
director, officer, employee or agent of another corporation, partnership, joint
venture, trust, or other enterprise, against expenses (including attorneys'
fees), judgments, fines and amounts paid in settlement actually and reasonably
incurred by him in connection with such action, suit or proceeding if he acted
in good faith and in a manner he reasonably believed to be in or not opposed to
the best interests of the Registrant, and with respect to any criminal action or
proceeding, had no reasonable cause to believe his conduct was unlawful;
provided, however, no indemnification shall be made in connection with any
proceeding brought by or in the right of the Registrant where the person
involved is adjudged to be liable to the Registrant except to the extent
approved by a court. Article NINTH of the Registrant's Restated Certificate of
Incorporation and Article VII of the Registrant's Restated By-laws provide that
the Registrant shall, to the fullest extent permitted by applicable law,
indemnify each person who was or is a party or is threatened to be made a party
to any threatened, pending or completed action, suit, or proceeding by reason of
the fact that he is or was, or has agreed to become, a director or officer of
the Registrant, or is or was serving at the written request of the Registrant,
as a director, officer or trustee of, or in a similar capacity with, another
corporation, partnership, joint venture, trust, or other enterprise. The
indemnification provided for in each of Article NINTH and Article VII is
expressly not exclusive of any other rights to which those seeking
indemnification may be entitled under any law, agreement, or vote of
stockholders or disinterested directors or otherwise, and shall inure to the
benefit of the heirs, executors, and administrators of such persons. Article VII
also provides that the Registrant shall have the power to purchase and maintain
insurance on behalf of any person who is or was a director, officer, employee,
or agent of the Registrant, or is or was serving at the request of the
Registrant, as a director, trustee, partner, officer, employee, or agent of
another corporation, partnership, joint venture, trust, or other enterprise,
against any liability asserted against and incurred by such person in any such
capacity.

          Pursuant to Section 102(b)(7) of the Delaware General Corporation
Laws, Article EIGHTH of the Registrant's Restated Certificate of Incorporation
eliminates a director's personal liability for monetary damages to the
Registrant and its stockholders for breaches of fiduciary duty as a director,
except in circumstances involving a breach of a director's duty of loyalty to
the Registrant or its stockholders, acts or omissions not in good faith or which
involve intentional misconduct or knowing violation of the law, self-dealing, or
the unlawful payment of dividends or repurchase of stock.

          The Registrant maintains an insurance policy on behalf of itself and
certain of its subsidiaries, and on behalf of the directors and officers
thereof, covering certain liabilities which may arise as a result of the actions
of the directors and officers.

          The Registrant has entered into agreements with all of its directors
affirming the Registrant's obligation to indemnify them to the fullest extent
permitted by law and providing various other protections.

     Item 7.  Exemption from Registration Claimed
              -----------------------------------

          Not applicable.

                                      -2-
<PAGE>

     Item 8.  Exhibits
              --------

          The Exhibit Index immediately preceding the exhibits is incorporated
herein by reference.

     Item 9.  Undertakings
              ------------

          1.  The undersigned Registrant hereby undertakes:

               (1) To file, during any period in which offers or sales are being
     made, a post-effective amendment to this Registration Statement:

                   (i)  To include any prospectus required by Section 10(a)(3)
                        of the Securities Act;

                   (ii) To reflect in the prospectus any facts or events arising
                        after the effective date of the Registration Statement
                        (or the most recent post-effective amendment thereof)
                        which, individually or in the aggregate, represent a
                        fundamental change in the information set forth in the
                        Registration Statement; and

                  (iii) To include any material information with respect to the
                        plan of distribution not previously disclosed in the
                        Registration Statement or any material change to such
                        information in the Registration Statement;

               provided, however, that paragraphs (i) and (ii) do not apply if
     the information required to be included in a post-effective amendment by
     those paragraphs is contained in periodic reports filed with or furnished
     to the Commission by the Registrant pursuant to Section 13 or 15(d) of the
     Exchange Act that are incorporated by reference in the Registration
     Statement.

               (2) That, for the purpose of determining any liability under the
     Securities Act, each such post-effective amendment shall be deemed to be a
     new Registration Statement relating to the securities offered therein, and
     the offering of such securities at that time shall be deemed to be the
     initial bona fide offering thereof.

               (3)   To remove from registration by means of a post-effective
     amendment any of the securities being registered which remain unsold at the
     termination of the offering.

          2.  The undersigned Registrant hereby undertakes that, for purposes of
determining any liability under the Securities Act, each filing of the
Registrant's annual report pursuant to Section 13(a) or 15(d) of the Exchange
Act (and, where applicable, each filing of an employee benefit plan's annual
report pursuant to Section 15(d) of the Exchange Act) that is incorporated by
reference in the Registration Statement shall be deemed to be a new Registration
Statement relating to the securities offered therein, and the offering of such
securities at that time shall be deemed to be the initial bona fide offering
thereof.

          3.    Insofar as indemnification for liabilities arising under the
Securities Act may be permitted to directors, officers and controlling persons
of the Registrant pursuant to the foregoing provisions, or otherwise, the
Registrant has been advised that in the opinion of the Commission such
indemnification is against public policy as expressed in the Securities Act and
is, therefore, unenforceable.  In the event that a claim for indemnification
against such liabilities (other than the payment by the Registrant of expenses
incurred or paid by a director, officer or controlling person of the

                                      -3-
<PAGE>

Registrant in the successful defense of any action, suit or proceeding) is
asserted by such director, officer or controlling person in connection with the
securities being registered, the Registrant will, unless in the opinion of its
counsel the matter has been settled by controlling precedent, submit to a court
of appropriate jurisdiction the question whether such indemnification by it is
against public policy as expressed in the Securities Act and will be governed by
the final adjudication of such issue.

                                      -4-
<PAGE>

                                   SIGNATURES

Pursuant to the requirements of the Securities Act, the Registrant certifies
that it has reasonable grounds to believe that it meets all of the requirements
for filing on Form S-8 and has duly caused this Registration Statement to be
signed on its behalf by the undersigned, thereunto duly authorized, in the Town
of Andover, Commonwealth of Massachusetts on January 11, 2000.

                                              CMGI, INC.

                                      By:  /s/David S. Wetherell
                                          ------------------------------------
                                          David S. Wetherell
                                          Chairman of the Board, President and
                                          Chief Executive Officer


                               POWER OF ATTORNEY

We, the undersigned officers and directors of CMGI, Inc. hereby severally
constitute David S. Wetherell, Andrew J. Hajducky, III and William Williams II,
and each of them singly, our true and lawful attorneys with full power to them,
and each of them singly, to sign for us and in our names in the capacities
indicated below, the Registration Statement on Form S-8 filed herewith and any
and all subsequent amendments to said Registration Statement, and generally to
do all such things in our names and behalf in our capacities as officers and
directors to enable CMGI, Inc. to comply with all requirements of the Securities
and Exchange Commission, hereby ratifying and confirming our signatures as they
may be signed by said attorneys, or any of them, to said Registration Statement
and any and all amendments thereto.

                                      -5-
<PAGE>

     Pursuant to the requirements of the Securities Act, this Registration
Statement has been signed by the following persons in the capacities and on the
dates indicated.

<TABLE>
<CAPTION>
Signature                                                    Title                            Date
----------------------------------------        --------------------------------  -----------------------------
<S>                                             <C>                               <C>
/s/David S. Wetherell                           Chairman of the Board of                January 11, 2000
----------------------------------------        Directors, President and Chief
David S. Wetherell                              Executive Officer (Principal
                                                Executive Officer)

/s/Andrew J. Hajducky, III                      Executive Vice President, Chief         January 11, 2000
----------------------------------------        Financial Officer and Treasurer
Andrew J. Hajducky, III                         (Principal Financial and
                                                Accounting Officer)

/s/William Berkman                              Director                                January 11, 2000
----------------------------------------
William Berkman
/s/Craig Goldman                                Director                                January 11, 2000
----------------------------------------
Craig Goldman
 /s/Avram Miller                                Director                                January 11, 2000
----------------------------------------
Avram Miller

/s/Robert Ranalli                               Director                                January 11, 2000
----------------------------------------
Robert Ranalli

/s/William D. Strecker                          Director                                January 11, 2000
----------------------------------------
William D. Strecker
</TABLE>

                                      -6-
<PAGE>

                                 EXHIBIT INDEX

Exhibit
 Number                            Description
--------                           -----------

  4.1     Specimen Certificate of Common Stock, $.01 par value per share, of
          the Registrant is incorporated herein by reference to Exhibit 4.1 to
          the Registrant's Annual Report on Form 10-K for the fiscal year ended
          July 31, 1999 (File No. 000-23262)

  5       Opinion of Hale and Dorr LLP

 23.1     Consent of Hale and Dorr LLP (included in Exhibit 5)

 23.2     Consent of KPMG LLP, independent accountants

 23.3     Consent of PricewaterhouseCoopers LLP, independent accountants

 23.4     Consent of Singer Lewak Greenbaum & Goldstein LLP, independent
          accountants

 23.5     Consent of Deloitte & Touche LLP, independent accoountants

 24       Power of Attorney (included in the signature pages of this
          Registration Statement)
[{"type": "S-8", "sequence": "1", "description": "FORM S-8", "secsgml_size_bytes": 19867}]
{"company-data": {"conformed-name": "CMGI INC", "cik": "0000914712", "assigned-sic": "7331", "irs-number": "042921333", "state-of-incorporation": "DE", "fiscal-year-end": "0731"}, "filing-values": {"form-type": "S-8", "act": "33", "file-number": "333-94479", "film-number": "505836"}, "business-address": {"street1": "100 BRICKSTONE SQUARE", "street2": "STE B110", "city": "ANDOVER", "state": "MA", "zip": "01810", "phone": "9786843600"}, "mail-address": {"street1": "100 BRICKSTONE SQUARE", "street2": "100 BRICKSTONE SQUARE", "city": "ANDOVER", "state": "MA", "zip": "01810"}, "former-company": {"former-conformed-name": "CMG INFORMATION SERVICES INC", "date-changed": "19981007"}}
As filed with the Securities and Exchange Commission on January 12, 2000
                                                 Registration No. 333- _________

                      SECURITIES AND EXCHANGE COMMISSION
                            Washington, D.C.  20549

                                   FORM S-8

                         REGISTRATION STATEMENT UNDER
                          THE SECURITIES ACT OF 1933

                                  CMGI, INC.
            (Exact Name of Registrant as Specified in Its Charter)

               DELAWARE                                        04-2921333
     (State or Other Jurisdiction of                        (I.R.S. Employer
     Incorporation or Organization)                       Identification Number)

     100 BRICKSTONE SQUARE, ANDOVER, MASSACHUSETTS               01810
       (Address of Principal Executive Offices)               (Zip Code)

                         ADFORCE, INC. 1997 STOCK PLAN
            ADFORCE, INC. STARPOINT SOFTWARE, INC. 1996 STOCK PLAN
                   ADFORCE, INC. 1999 EQUITY INCENTIVE PLAN
                ADFORCE, INC. 1999 EMPLOYEE STOCK PURCHASE PLAN
                ADFORCE, INC. 1999 DIRECTORS STOCK OPTION PLAN
                ADFORCE, INC. INCENTIVE STOCK OPTION AGREEMENTS

                           (Full Title of the Plan)

                              DAVID S. WETHERELL
                     PRESIDENT AND CHIEF EXECUTIVE OFFICER
                                  CMGI, INC.
                             100 BRICKSTONE SQUARE
                         Andover, Massachusetts  01810
                    (Name and Address of Agent for Service)

                                 (978) 684-3600
         (Telephone Number, Including Area Code, of Agent for Service)

                                   Copies to:

                           WILLIAM WILLIAMS II, ESQ.
                       VICE PRESIDENT AND GENERAL COUNSEL
                                   CMGI, INC.
                             100 BRICKSTONE SQUARE
                         Andover, Massachusetts  01810

                        CALCULATION OF REGISTRATION FEE
Proposed Maximum       Proposed Maximum
       Title of             Amount            Offering          Aggregate Offering        Amount of
      Securities            to be               Price                 Price             Registration
        to be             Registered          Per Share                                      Fee
      Registered
----------------------  -------------     ----------------      ------------------      ------------
Common Stock, $.01        1,972,488            $129.67(1)           $255,772,519(1)       $67,524
 par value                  shares
--------------------------------------------------------------------------------------------------------
(1)  Estimated solely for the purpose of calculating the registration fee, and
     based on the average of the high and low prices of the Common Stock on the
     Nasdaq National Market on January 7, 2000 in accordance with Rules 457(c)
     and 457(h) under the Securities Act of 1933.
PART I.  INFORMATION REQUIRED IN THE SECTION 10(a) PROSPECTUS

          The information required by Part I is included in documents sent or
given to participants in the Registrant's AdForce, Inc. 1997 Stock Plan,
AdForce, Inc. Starpoint Software, Inc. 1996 Stock Plan, AdForce, Inc. 1999
Equity Incentive Plan, AdForce, Inc.1999 Employee Stock Purchase Plan, AdForce,
Inc. 1999 Directors Stock Option Plan and AdForce, Inc. Incentive Stock Option
Agreements, pursuant to Rule 428(b)(1) of the Securities Act of 1933, as
amended (the "Securities Act").

PART II.  INFORMATION REQUIRED IN THE REGISTRATION STATEMENT

     Item 3.  Incorporation of Documents by Reference
              ---------------------------------------

          The Registrant is subject to the informational and reporting
requirements of Sections 13(a), 14 and 15(d) of the Securities Exchange Act of
1934, as amended (the "Exchange Act"), and in accordance therewith files
reports, proxy statements and other information with the Securities and Exchange
Commission (the "Commission").  The following documents, which are on file with
the Commission, are incorporated in this Registration Statement by reference:

          (1)  The Registrant's latest annual report filed pursuant to Section
               13(a) or 15(d) of the Exchange Act, or the latest prospectus
               filed pursuant to Rule 424(b) under the Securities Act that
               contains audited financial statements for the Registrant's latest
               fiscal year for which such statements have been filed.

          (2)  All other reports filed pursuant to Section 13(a) or 15(d) of the
               Exchange Act since the end of the fiscal year covered by the
               document referred to in (1) above.

          (3)  The description of the common stock of the Registrant, $.01 par
               value per share (the "Common Stock"), contained in a registration
               statement filed under the Exchange Act, including any amendment
               or report filed for the purpose of updating such description.

          All documents subsequently filed by the Registrant pursuant to
Sections 13(a), 13(c), 14 and 15(d) of the Exchange Act, prior to the filing of
a post-effective amendment which indicates that all shares of Common Stock
offered hereby have been sold or which deregisters all shares of Common Stock
then remaining unsold, shall be deemed to be incorporated by reference herein
and to be part hereof from the date of the filing of such documents.  Any
statement contained in a document incorporated or deemed to be incorporated by
reference herein shall be deemed to be modified or superseded for purposes of
this Registration Statement to the extent that a statement contained herein or
in any other subsequently filed document which also is or is deemed to be
incorporated by reference herein modifies or supersedes such statement.  Any
statement so modified or superseded shall not be deemed, except as so modified
or superseded, to constitute a part of this Registration Statement.

     Item 4.  Description of Securities
              -------------------------

          Not applicable.

     Item 5.  Interests of Named Experts and Counsel
              --------------------------------------

          The legality of the Common Stock being offered hereby will be passed
for the Registrant by Hale and Dorr LLP, Boston, Massachusetts. Certain partners
of Hale and Dorr LLP and their affiliates beneficially own an aggregate of 3,150
shares of Common Stock of the Registrant.
Item 6.  Indemnification of Directors and Officers
                   -----------------------------------------

          Section 145 of the Delaware General Corporation Law grants the
Registrant the power to indemnify each person who was or is a party or is
threatened to be made a party to any threatened, pending or completed action,
suit, or proceeding, whether civil, criminal, administrative, or investigative
by reason of the fact that he is or was a director, officer, employee or agent
of the Registrant, or is or was serving at the request of the Registrant as a
director, officer, employee or agent of another corporation, partnership, joint
venture, trust, or other enterprise, against expenses (including attorneys'
fees), judgments, fines and amounts paid in settlement actually and reasonably
incurred by him in connection with such action, suit or proceeding if he acted
in good faith and in a manner he reasonably believed to be in or not opposed to
the best interests of the Registrant, and with respect to any criminal action or
proceeding, had no reasonable cause to believe his conduct was unlawful;
provided, however, no indemnification shall be made in connection with any
proceeding brought by or in the right of the Registrant where the person
involved is adjudged to be liable to the Registrant except to the extent
approved by a court. Article NINTH of the Registrant's Restated Certificate of
Incorporation and Article VII of the Registrant's Restated By-laws provide that
the Registrant shall, to the fullest extent permitted by applicable law,
indemnify each person who was or is a party or is threatened to be made a party
to any threatened, pending or completed action, suit, or proceeding by reason of
the fact that he is or was, or has agreed to become, a director or officer of
the Registrant, or is or was serving at the written request of the Registrant,
as a director, officer or trustee of, or in a similar capacity with, another
corporation, partnership, joint venture, trust, or other enterprise. The
indemnification provided for in each of Article NINTH and Article VII is
expressly not exclusive of any other rights to which those seeking
indemnification may be entitled under any law, agreement, or vote of
stockholders or disinterested directors or otherwise, and shall inure to the
benefit of the heirs, executors, and administrators of such persons. Article VII
also provides that the Registrant shall have the power to purchase and maintain
insurance on behalf of any person who is or was a director, officer, employee,
or agent of the Registrant, or is or was serving at the request of the
Registrant, as a director, trustee, partner, officer, employee, or agent of
another corporation, partnership, joint venture, trust, or other enterprise,
against any liability asserted against and incurred by such person in any such
capacity.

          Pursuant to Section 102(b)(7) of the Delaware General Corporation
Laws, Article EIGHTH of the Registrant's Restated Certificate of Incorporation
eliminates a director's personal liability for monetary damages to the
Registrant and its stockholders for breaches of fiduciary duty as a director,
except in circumstances involving a breach of a director's duty of loyalty to
the Registrant or its stockholders, acts or omissions not in good faith or which
involve intentional misconduct or knowing violation of the law, self-dealing, or
the unlawful payment of dividends or repurchase of stock.

          The Registrant maintains an insurance policy on behalf of itself and
certain of its subsidiaries, and on behalf of the directors and officers
thereof, covering certain liabilities which may arise as a result of the actions
of the directors and officers.

          The Registrant has entered into agreements with all of its directors
affirming the Registrant's obligation to indemnify them to the fullest extent
permitted by law and providing various other protections.

     Item 7.  Exemption from Registration Claimed
              -----------------------------------

          Not applicable.

                                      -2-
Item 8.  Exhibits
              --------

          The Exhibit Index immediately preceding the exhibits is incorporated
herein by reference.

     Item 9.  Undertakings
              ------------

          1.  The undersigned Registrant hereby undertakes:

               (1) To file, during any period in which offers or sales are being
     made, a post-effective amendment to this Registration Statement:

                   (i)  To include any prospectus required by Section 10(a)(3)
                        of the Securities Act;

                   (ii) To reflect in the prospectus any facts or events arising
                        after the effective date of the Registration Statement
                        (or the most recent post-effective amendment thereof)
                        which, individually or in the aggregate, represent a
                        fundamental change in the information set forth in the
                        Registration Statement; and

                  (iii) To include any material information with respect to the
                        plan of distribution not previously disclosed in the
                        Registration Statement or any material change to such
                        information in the Registration Statement;

               provided, however, that paragraphs (i) and (ii) do not apply if
     the information required to be included in a post-effective amendment by
     those paragraphs is contained in periodic reports filed with or furnished
     to the Commission by the Registrant pursuant to Section 13 or 15(d) of the
     Exchange Act that are incorporated by reference in the Registration
     Statement.

               (2) That, for the purpose of determining any liability under the
     Securities Act, each such post-effective amendment shall be deemed to be a
     new Registration Statement relating to the securities offered therein, and
     the offering of such securities at that time shall be deemed to be the
     initial bona fide offering thereof.

               (3)   To remove from registration by means of a post-effective
     amendment any of the securities being registered which remain unsold at the
     termination of the offering.

          2.  The undersigned Registrant hereby undertakes that, for purposes of
determining any liability under the Securities Act, each filing of the
Registrant's annual report pursuant to Section 13(a) or 15(d) of the Exchange
Act (and, where applicable, each filing of an employee benefit plan's annual
report pursuant to Section 15(d) of the Exchange Act) that is incorporated by
reference in the Registration Statement shall be deemed to be a new Registration
Statement relating to the securities offered therein, and the offering of such
securities at that time shall be deemed to be the initial bona fide offering
thereof.

          3.    Insofar as indemnification for liabilities arising under the
Securities Act may be permitted to directors, officers and controlling persons
of the Registrant pursuant to the foregoing provisions, or otherwise, the
Registrant has been advised that in the opinion of the Commission such
indemnification is against public policy as expressed in the Securities Act and
is, therefore, unenforceable.  In the event that a claim for indemnification
against such liabilities (other than the payment by the Registrant of expenses
incurred or paid by a director, officer or controlling person of the

                                      -3-
Registrant in the successful defense of any action, suit or proceeding) is
asserted by such director, officer or controlling person in connection with the
securities being registered, the Registrant will, unless in the opinion of its
counsel the matter has been settled by controlling precedent, submit to a court
of appropriate jurisdiction the question whether such indemnification by it is
against public policy as expressed in the Securities Act and will be governed by
the final adjudication of such issue.

                                      -4-
SIGNATURES

Pursuant to the requirements of the Securities Act, the Registrant certifies
that it has reasonable grounds to believe that it meets all of the requirements
for filing on Form S-8 and has duly caused this Registration Statement to be
signed on its behalf by the undersigned, thereunto duly authorized, in the Town
of Andover, Commonwealth of Massachusetts on January 11, 2000.

                                              CMGI, INC.

                                      By:  /s/David S. Wetherell
                                          ------------------------------------
                                          David S. Wetherell
                                          Chairman of the Board, President and
                                          Chief Executive Officer

                               POWER OF ATTORNEY

We, the undersigned officers and directors of CMGI, Inc. hereby severally
constitute David S. Wetherell, Andrew J. Hajducky, III and William Williams II,
and each of them singly, our true and lawful attorneys with full power to them,
and each of them singly, to sign for us and in our names in the capacities
indicated below, the Registration Statement on Form S-8 filed herewith and any
and all subsequent amendments to said Registration Statement, and generally to
do all such things in our names and behalf in our capacities as officers and
directors to enable CMGI, Inc. to comply with all requirements of the Securities
and Exchange Commission, hereby ratifying and confirming our signatures as they
may be signed by said attorneys, or any of them, to said Registration Statement
and any and all amendments thereto.

                                      -5-
Pursuant to the requirements of the Securities Act, this Registration
Statement has been signed by the following persons in the capacities and on the
dates indicated.
Signature                                                    Title                            Date
----------------------------------------        --------------------------------  -----------------------------
/s/David S. Wetherell                           Chairman of the Board of                January 11, 2000
----------------------------------------        Directors, President and Chief
David S. Wetherell                              Executive Officer (Principal
                                                Executive Officer)

/s/Andrew J. Hajducky, III                      Executive Vice President, Chief         January 11, 2000
----------------------------------------        Financial Officer and Treasurer
Andrew J. Hajducky, III                         (Principal Financial and
                                                Accounting Officer)

/s/William Berkman                              Director                                January 11, 2000
----------------------------------------
William Berkman
/s/Craig Goldman                                Director                                January 11, 2000
----------------------------------------
Craig Goldman
 /s/Avram Miller                                Director                                January 11, 2000
----------------------------------------
Avram Miller

/s/Robert Ranalli                               Director                                January 11, 2000
----------------------------------------
Robert Ranalli

/s/William D. Strecker                          Director                                January 11, 2000
----------------------------------------
William D. Strecker
-6-
EXHIBIT INDEX

Exhibit
 Number                            Description
--------                           -----------

  4.1     Specimen Certificate of Common Stock, $.01 par value per share, of
          the Registrant is incorporated herein by reference to Exhibit 4.1 to
          the Registrant's Annual Report on Form 10-K for the fiscal year ended
          July 31, 1999 (File No. 000-23262)

  5       Opinion of Hale and Dorr LLP

 23.1     Consent of Hale and Dorr LLP (included in Exhibit 5)

 23.2     Consent of KPMG LLP, independent accountants

 23.3     Consent of PricewaterhouseCoopers LLP, independent accountants

 23.4     Consent of Singer Lewak Greenbaum & Goldstein LLP, independent
          accountants

 23.5     Consent of Deloitte & Touche LLP, independent accoountants

 24       Power of Attorney (included in the signature pages of this
          Registration Statement)