<PAGE>

As filed with the Securities and Exchange Commission on April 19, 2001.

                                                   Registration No. 333-________

================================================================================

                       SECURITIES AND EXCHANGE COMMISSION
                             WASHINGTON, DC. 20549

                                    FORM S-8

                          REGISTRATION STATEMENT UNDER
                           THE SECURITIES ACT OF 1933

                            MERCATOR SOFTWARE, INC.
             (Exact name of registrant as specified in its charter)

               Delaware                                   06-1132156
     (State or other jurisdiction of                  (I.R.S. Employer
      incorporation or organization)                 Identification No.)

                                45 Danbury Road
                           Wilton, Connecticut 06897
                                 (203) 761-8600
              (Address of Principal Executive Offices) (Zip Code)

                         _____________________________

                           1997 Equity Incentive Plan
                            (Full title of the plan)

                         _____________________________

                                  Roy C. King
                            Chief Executive Officer
                            Mercator Software, Inc.
                                45 Danbury Road
                           Wilton, Connecticut 06897
                                 (203) 761-8600
           (Name and address including zip code and telephone number,
                   including area code, of agent for service)

                         _____________________________

                                   Copies to:

                             Heather S. Stone, Esq.
                        TESTA, HURWITZ & THIBEAULT, LLP
                                125 High Street
                          Boston, Massachusetts 02110
                                 (617) 248-7000

================================================================================
<PAGE>

                                      -2-

<TABLE>
<CAPTION>
                                              CALCULATION OF REGISTRATION FEE

===========================================================================================================================

                                                           Proposed maximum        Proposed maximum
     Title of securities             Amount to be              offering               aggregate             Amount of
       to be registered            registered/(1)/          price per share          offering price       registration fee
       ----------------            ---------------          ---------------          --------------       ----------------
<S>                                    <C>                     <C>                <C>                       <C>
1997 Equity Incentive Plan

Common Stock, par value
$.01  per share

                                         194,035(2)              $1.68            $325,978.80               $81.49
                                         250,000(3)              $9.188           $2,297,000.00             $574.25
                                         250,000(3)              $4.375           $1,093,750.00             $273.44
                                          21,000(3)              $7.875           $165,375.00               $41.34
                                           1,000(3)              $9.938           $9,938.00                 $2.48
                                           2,750(3)              $10.25           $28,187.50                $7.05
                                           2,000(3)              $10.063          $20,126.00                $5.03
                                          38,000(3)              $10.313          $391,894.00               $97.97
                                           3,000(3)              $8.938           $26,814.00                $6.70
                                           2,250(3)              $8.00            $18,000.00                $4.50
                                         270,000(3)              $8.00            $2,160,000.00             $540.00
                                           1,000(3)              $6.938           $6,938.00                 $1.73
                                         608,750(3)              $4.75            $2,891,562.50             $722.89
                                          24,100(3)              $4.688           $112,980.80               $28.25
                                          10,000(3)              $4.125           $41,250.00                $10.31
                                          44,250(3)              $4.281           $189,434.25               $47.36
                                             500(1)              $4.875           $2,437.50                 $0.61
                                          15,000(3)              $4.188           $62,820.00                $15.71
                                           5,000(2)              $2.96            $14,800.00                $3.70
                                           8,200(3)              $3.313           $27,166.60                $6.79
                                         199,165(2)              $3.375           $672,181.88               $168.05
TOTAL                                  1,950,000
===========================================================================================================================
</TABLE>


/(1)/  Upon the filing and effectiveness of this amendment to Registration
       Statement on Form S-8, the total number of shares of Common Stock
       registered pursuant to the 1997 Equity Incentive Plan will be 6,700,000,
       plus such additional shares as may be required pursuant to the plan in
       the event of a stock dividend, split-up of shares, recapitalization or
       other similar change in the Common Stock.

/(2)/  Pursuant to Rule 457(c) and (h)(1) of Regulation C of the Securities Act,
       the price of $1.68 per share, is the average of the high and low prices
       of the Common Stock as reported on The Nasdaq National Market on
       April 16, 2001 and is set forth solely for purposes of calculating
       the filing fee for those shares without a fixed exercise price.

/(3)/  Such shares are issuable upon the exercise of outstanding options with
       fixed exercise prices. Pursuant to Rule 457(h), the aggregate offering
       price and the fee have been computed upon the basis of the price at which
       the options may be exercised. The offering price per share set forth for
       such shares is the exercise price per share at which such options are
       exercisable.
<PAGE>

                                      -3-

     This Registration Statement registers additional securities of the same
class as other securities for which (i) Registration Statement No. 333-30631 on
Form S-8 as filed with the Securities and Exchange Commission (the "Commission")
on July 2, 1997, relating to the Registrant's 1997 Employee Stock Purchase Plan,
is effective; (ii) Registration Statement No. 333-37969 on Form S-8 as filed
with the Commission on October 15, 1997, relating to the Registrant's 1997
Equity Incentive Plan and 1997 Director's Stock Option Plan, is effective; (iii)
Registration Statement No. 333-89951 on Form S-8 as filed with the Commission on
October 29, 1999, relating to Novera Software, Inc.'s 1996 Stock Option Plan, is
effective; and (iv) Registration Statement No. 333-32002 on Form S-8 as filed
with the Commission on March 8, 2000, relating to the Registrant's 1997 Equity
Incentive Plan, is effective. Pursuant to General Instruction E to Form S-8, the
contents of the above-listed Registration Statements are hereby incorporated by
reference.

                                    PART II

               INFORMATION REQUIRED IN THE REGISTRATION STATEMENT

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

     The following documents filed by Mercator Software, Inc. (the "Registrant")
with the Commission pursuant to the Securities Exchange Act of 1934, as amended
(the "Exchange Act"), are incorporated in this Registration Statement by
reference as of their respective dates:

     (a)  The Registrant's Annual Report on Form 10-K for the fiscal year ended
          December 31, 2000, filed with the Commission on March 30, 2001; and

     (b)  The section entitled "Description of Registrant's Securities to be
          Registered" contained in the Registrant's registration statement on
          Form 8-A filed with the Commission on June 6, 1997 pursuant to Section
          12(g) of the Exchange Act and incorporating by reference the
          information contained in the Registrant's Registration Statement on
          Form S-1 (SEC File No. 333-27293) initially filed with the Commission
          on March 6, 1997 as amended.

     All documents subsequently filed with the Commission 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 securities
offered herein have been sold or which deregisters all securities then remaining
unsold, shall be deemed to be incorporated by reference in this Registration
Statement and to be a part hereof from the date of filing of such documents.
<PAGE>

                                      -4-

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

     Exhibit No.                        Description of Exhibit
     -----------                        ----------------------

           4.1              Amended and Restated Certificate of Incorporation,
                            as amended, of the Registrant (filed as Exhibit 3.1
                            to the Registrant's Quarterly Report on Form 10-Q on
                            November 14, 2000, File No. 000-22667 (7674707), and
                            incorporated by reference herein).*

           4.2              Amended and Restated By-Laws of the Registrant
                            (filed as Exhibit 3.1 to the Registrant's
                            Registration Statement on Form 8-A on September 4,
                            1998, File No. 000-22667 (98704715), and
                            incorporated by reference herein).*

           4.3              1997 Equity Incentive Plan, as amended, of the
                            Registrant (filed as Exhibit 4.06 to the
                            Registrant's Registration Statement on Form S-8 on
                            October 15, 1997, File No. 333-37969, and
                            incorporated by reference herein).*

           4.4              Certificate of Designation specifying the terms of
                            the Series A Junior Participating Preferred Stock of
                            the Registrant (filed as Exhibit 3.2 to the
                            Registrant's Registration Statement on Form 8-A on
                            September 4, 1998, File No. 000-22667 (98704715),
                            and incorporated by reference herein).*

           4.5              Rights Agreement dated September 2, 1998 between the
                            Registrant and the Bank of New York (filed as
                            Exhibit 3.3 to the Registrant's Registration
                            Statement on Form 8-A on September 4, 1998, File No.
                            000-22667 (98704715), and incorporated by reference
                            herein).*

           5.1              Opinion of Testa, Hurwitz & Thibeault, LLP.**

          23.1              Consent of Testa, Hurwitz & Thibeault, LLP
                            (contained in its opinion as Exhibit 5.1).

          23.2              Consent of KPMG, LLP.**

          24.1              Power of Attorney (included as part of the signature
                            page of this Registration Statement).

     *Not-filed herewith. In accordance with Rule 411 promulgated pursuant to
the Securities Act of 1933, as amended, reference is made to the documents
previously filed with the commission, which are incorporated by reference
herein.
     **Filed herewith.

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

          (a)  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:


<PAGE>

                                      -5-

               (i)   To include any prospectus required by Section 10(a)(3) of
                     the Securities Act of 1933;

               (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 (a) (1) (i) and (a) (1) (ii) do
               not apply if the registration statement is on Form S-3, Form S-8
               or Form F-3, and 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 Securities
               Exchange Act of 1934 that are incorporated by reference in the
               registration statement.

          (2)  That, for the purpose of determining any liability under the
               Securities Act of 1933, 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.

     (b)  The undersigned Registrant hereby undertakes that, for purposes of
          determining any liability under the Securities Act of 1933, each
          filing of the Registrant's annual report pursuant to Section 13(a) or
          Section 15(d) of the Securities Exchange Act of 1934 (and, where
          applicable, each filing of any employee benefit plan's annual report
          pursuant to Section 15(d) of the Securities Exchange Act of 1934) 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.

     (c)  Insofar as indemnification for liabilities arising under the
          Securities Act of 1933 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 Securities and Exchange Commission such indemnification
          is against public policy as expressed in the 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
          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 Act and will be
          governed by the final adjudication of such issue.
<PAGE>

                                      -6-

                                  SIGNATURES

Pursuant to the requirements of the Securities Act of 1933, 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 City of Wilton, the State of Connecticut, on this 19th day of
April 2001.

                                        MERCATOR SOFTWARE, INC.

                                        By: /s/ Roy C. King
                                           ----------------------------
                                           Roy C. King
                                           President and Chief Executive Officer

                                POWER OF ATTORNEY

          EACH SUCH PERSON WHOSE SIGNATURE appears below constitutes and
appoints, jointly and severally, Roy C. King and Richard Applegate and each of
them, with full power to act without the other, his true and lawful attorney-in-
fact and agent, with the power of substitution and resubstitution, for him and
in his name, place and stead, in any and all capacities, to sign any amendments
to this Registration Statement on Form S-8 (including post-effective amendments)
and to file the same, with all exhibits thereto, and other documents in
connection therewith, with the Securities and Exchange Commission, hereby
ratifying and confirming all that said attorney-in-fact, or his or her
substitute or substitutes, may do or cause to be done by virtue hereof.

          Pursuant to the requirements of the Securities Act of 1933, this
Registration Statement has been signed by the following persons in the
capacities and on the date indicated.

<TABLE>
<CAPTION>
             Signature                                Title                                         Date
             ---------                                -----                                         ----
<S>                                   <C>                                                     <C>
  /s/ Roy C. King
---------------------------------     President, Chief Executive Officer                      April 19, 2001
  Roy C. King                         and Director

  /s/ Richard Applegate
---------------------------------     Vice President, Finance and                             April 19, 2001
  Richard Applegate                   Accounting and Chief Financial Officer

  /s/ James P. Schadt
---------------------------------     Chairman of the Board of Directors                      April 19, 2001
  James P. Schadt

  /s/ Diane P. Baker
---------------------------------     Director                                                April 19, 2001
  Diane P. Baker

  /s/ Constance F. Galley
---------------------------------     Director                                                April 19, 2001
  Constance F. Galley

  /s/ Ernest E. Keet
---------------------------------     Director                                                April 19, 2001
  Ernest E. Keet

  /s/ Richard Little
---------------------------------     Director                                                April 19, 2001
  Richard Little

  /s/ Dennis G. Sisco
---------------------------------     Director                                                April 19, 2001
  Dennis G. Sisco

  /s/ Mark Stevens
---------------------------------     Director                                                April 19, 2001
  Mark Stevens
</TABLE>
<PAGE>

                               INDEX TO EXHIBITS

       Exhibit                          Description of Exhibit
       -------                          ----------------------

          4.1           Amended and Restated Certificate of Incorporation, as
                        amended, of the Registrant (filed as Exhibit 3.1 to the
                        Registrant's Quarterly Report on Form  10-Q on November
                        14, 2000, File No. 000-22667 (7674707) and incorporated
                        by reference herein).*

          4.2           Amended and Restated By-Laws of the Registrant (filed
                        as Exhibit 3.1 to the Registrant's Registration
                        Statement on Form 8-A on September 4, 1998, File No.
                        000-22667 (98704715), and incorporated by reference
                        herein).*

          4.3           1997 Equity Incentive Plan, as amended, of the
                        Registrant (filed as Exhibit 4.06 to the Registrant's
                        Registration Statement on Form S-8 on October 15, 1997,
                        File No. 333-37969, and incorporated by reference
                        herein).*

          4.4           Certificate of Designation specifying the terms of the
                        Series A Junior Participating Preferred Stock of the
                        Registrant (filed as Exhibit 3.2 to the Registrant's
                        Registration Statement on Form 8-A on September 4,
                        1998, File No. 000-22667 (98704715), and incorporated
                        by reference herein).*

          4.5           Rights Agreement dated September 2, 1998 between the
                        Registrant and the Bank of New York (filed as Exhibit
                        3.3 to the Registrant's Registration Statement on Form
                        8-A on September 4, 1998, File No. 000-22667
                        (98704715), and incorporated by reference herein).*

          5.1           Opinion of Testa, Hurwitz & Thibeault, LLP.**

         23.1           Consent of Testa, Hurwitz & Thibeault, LLP (contained
                        in its opinion as Exhibit 5.1).

         23.2           Consent of KPMG, LLP.**

         24.1           Power of Attorney (included as part of the signature
                        page of this Registration Statement).

     *Not-filed herewith. In accordance with Rule 411 promulgated pursuant to
the Securities Act of 1933, as amended, reference is made to the documents
previously filed with the commission, which are incorporated by reference
herein.
     **Filed herewith.
[{"type": "S-8", "sequence": "1", "filename": "0001.txt", "description": "REGISTRATION STATEMENT", "secsgml_size_bytes": 23247}]
{"company-data": {"conformed-name": "MERCATOR SOFTWARE INC", "cik": "0001039276", "assigned-sic": "7372", "irs-number": "061132156", "state-of-incorporation": "DE", "fiscal-year-end": "1231"}, "filing-values": {"form-type": "S-8", "act": "33", "file-number": "333-59240", "film-number": "1606831"}, "business-address": {"street1": "45 DANBURY RD", "city": "WILTON", "state": "CT", "zip": "06897", "phone": "2037617600"}, "mail-address": {"street1": "45 DANBURY", "city": "WILTON", "state": "CT", "zip": "06897"}, "former-company": {"former-conformed-name": "TSI INTERNATIONAL SOFTWARE LTD", "date-changed": "19970514"}}
As filed with the Securities and Exchange Commission on April 19, 2001.

                                                   Registration No. 333-________

================================================================================

                       SECURITIES AND EXCHANGE COMMISSION
                             WASHINGTON, DC. 20549

                                    FORM S-8

                          REGISTRATION STATEMENT UNDER
                           THE SECURITIES ACT OF 1933

                            MERCATOR SOFTWARE, INC.
             (Exact name of registrant as specified in its charter)

               Delaware                                   06-1132156
     (State or other jurisdiction of                  (I.R.S. Employer
      incorporation or organization)                 Identification No.)

                                45 Danbury Road
                           Wilton, Connecticut 06897
                                 (203) 761-8600
              (Address of Principal Executive Offices) (Zip Code)

                         _____________________________

                           1997 Equity Incentive Plan
                            (Full title of the plan)

                         _____________________________

                                  Roy C. King
                            Chief Executive Officer
                            Mercator Software, Inc.
                                45 Danbury Road
                           Wilton, Connecticut 06897
                                 (203) 761-8600
           (Name and address including zip code and telephone number,
                   including area code, of agent for service)

                         _____________________________

                                   Copies to:

                             Heather S. Stone, Esq.
                        TESTA, HURWITZ & THIBEAULT, LLP
                                125 High Street
                          Boston, Massachusetts 02110
                                 (617) 248-7000

================================================================================
-2-
CALCULATION OF REGISTRATION FEE

===========================================================================================================================

                                                           Proposed maximum        Proposed maximum
     Title of securities             Amount to be              offering               aggregate             Amount of
       to be registered            registered/(1)/          price per share          offering price       registration fee
       ----------------            ---------------          ---------------          --------------       ----------------
1997 Equity Incentive Plan

Common Stock, par value
$.01  per share

                                         194,035(2)              $1.68            $325,978.80               $81.49
                                         250,000(3)              $9.188           $2,297,000.00             $574.25
                                         250,000(3)              $4.375           $1,093,750.00             $273.44
                                          21,000(3)              $7.875           $165,375.00               $41.34
                                           1,000(3)              $9.938           $9,938.00                 $2.48
                                           2,750(3)              $10.25           $28,187.50                $7.05
                                           2,000(3)              $10.063          $20,126.00                $5.03
                                          38,000(3)              $10.313          $391,894.00               $97.97
                                           3,000(3)              $8.938           $26,814.00                $6.70
                                           2,250(3)              $8.00            $18,000.00                $4.50
                                         270,000(3)              $8.00            $2,160,000.00             $540.00
                                           1,000(3)              $6.938           $6,938.00                 $1.73
                                         608,750(3)              $4.75            $2,891,562.50             $722.89
                                          24,100(3)              $4.688           $112,980.80               $28.25
                                          10,000(3)              $4.125           $41,250.00                $10.31
                                          44,250(3)              $4.281           $189,434.25               $47.36
                                             500(1)              $4.875           $2,437.50                 $0.61
                                          15,000(3)              $4.188           $62,820.00                $15.71
                                           5,000(2)              $2.96            $14,800.00                $3.70
                                           8,200(3)              $3.313           $27,166.60                $6.79
                                         199,165(2)              $3.375           $672,181.88               $168.05
TOTAL                                  1,950,000
===========================================================================================================================
/(1)/  Upon the filing and effectiveness of this amendment to Registration
       Statement on Form S-8, the total number of shares of Common Stock
       registered pursuant to the 1997 Equity Incentive Plan will be 6,700,000,
       plus such additional shares as may be required pursuant to the plan in
       the event of a stock dividend, split-up of shares, recapitalization or
       other similar change in the Common Stock.

/(2)/  Pursuant to Rule 457(c) and (h)(1) of Regulation C of the Securities Act,
       the price of $1.68 per share, is the average of the high and low prices
       of the Common Stock as reported on The Nasdaq National Market on
       April 16, 2001 and is set forth solely for purposes of calculating
       the filing fee for those shares without a fixed exercise price.

/(3)/  Such shares are issuable upon the exercise of outstanding options with
       fixed exercise prices. Pursuant to Rule 457(h), the aggregate offering
       price and the fee have been computed upon the basis of the price at which
       the options may be exercised. The offering price per share set forth for
       such shares is the exercise price per share at which such options are
       exercisable.
-3-

     This Registration Statement registers additional securities of the same
class as other securities for which (i) Registration Statement No. 333-30631 on
Form S-8 as filed with the Securities and Exchange Commission (the "Commission")
on July 2, 1997, relating to the Registrant's 1997 Employee Stock Purchase Plan,
is effective; (ii) Registration Statement No. 333-37969 on Form S-8 as filed
with the Commission on October 15, 1997, relating to the Registrant's 1997
Equity Incentive Plan and 1997 Director's Stock Option Plan, is effective; (iii)
Registration Statement No. 333-89951 on Form S-8 as filed with the Commission on
October 29, 1999, relating to Novera Software, Inc.'s 1996 Stock Option Plan, is
effective; and (iv) Registration Statement No. 333-32002 on Form S-8 as filed
with the Commission on March 8, 2000, relating to the Registrant's 1997 Equity
Incentive Plan, is effective. Pursuant to General Instruction E to Form S-8, the
contents of the above-listed Registration Statements are hereby incorporated by
reference.

                                    PART II

               INFORMATION REQUIRED IN THE REGISTRATION STATEMENT

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

     The following documents filed by Mercator Software, Inc. (the "Registrant")
with the Commission pursuant to the Securities Exchange Act of 1934, as amended
(the "Exchange Act"), are incorporated in this Registration Statement by
reference as of their respective dates:

     (a)  The Registrant's Annual Report on Form 10-K for the fiscal year ended
          December 31, 2000, filed with the Commission on March 30, 2001; and

     (b)  The section entitled "Description of Registrant's Securities to be
          Registered" contained in the Registrant's registration statement on
          Form 8-A filed with the Commission on June 6, 1997 pursuant to Section
          12(g) of the Exchange Act and incorporating by reference the
          information contained in the Registrant's Registration Statement on
          Form S-1 (SEC File No. 333-27293) initially filed with the Commission
          on March 6, 1997 as amended.

     All documents subsequently filed with the Commission 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 securities
offered herein have been sold or which deregisters all securities then remaining
unsold, shall be deemed to be incorporated by reference in this Registration
Statement and to be a part hereof from the date of filing of such documents.
-4-

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

     Exhibit No.                        Description of Exhibit
     -----------                        ----------------------

           4.1              Amended and Restated Certificate of Incorporation,
                            as amended, of the Registrant (filed as Exhibit 3.1
                            to the Registrant's Quarterly Report on Form 10-Q on
                            November 14, 2000, File No. 000-22667 (7674707), and
                            incorporated by reference herein).*

           4.2              Amended and Restated By-Laws of the Registrant
                            (filed as Exhibit 3.1 to the Registrant's
                            Registration Statement on Form 8-A on September 4,
                            1998, File No. 000-22667 (98704715), and
                            incorporated by reference herein).*

           4.3              1997 Equity Incentive Plan, as amended, of the
                            Registrant (filed as Exhibit 4.06 to the
                            Registrant's Registration Statement on Form S-8 on
                            October 15, 1997, File No. 333-37969, and
                            incorporated by reference herein).*

           4.4              Certificate of Designation specifying the terms of
                            the Series A Junior Participating Preferred Stock of
                            the Registrant (filed as Exhibit 3.2 to the
                            Registrant's Registration Statement on Form 8-A on
                            September 4, 1998, File No. 000-22667 (98704715),
                            and incorporated by reference herein).*

           4.5              Rights Agreement dated September 2, 1998 between the
                            Registrant and the Bank of New York (filed as
                            Exhibit 3.3 to the Registrant's Registration
                            Statement on Form 8-A on September 4, 1998, File No.
                            000-22667 (98704715), and incorporated by reference
                            herein).*

           5.1              Opinion of Testa, Hurwitz & Thibeault, LLP.**

          23.1              Consent of Testa, Hurwitz & Thibeault, LLP
                            (contained in its opinion as Exhibit 5.1).

          23.2              Consent of KPMG, LLP.**

          24.1              Power of Attorney (included as part of the signature
                            page of this Registration Statement).

     *Not-filed herewith. In accordance with Rule 411 promulgated pursuant to
the Securities Act of 1933, as amended, reference is made to the documents
previously filed with the commission, which are incorporated by reference
herein.
     **Filed herewith.

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

          (a)  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:
-5-

               (i)   To include any prospectus required by Section 10(a)(3) of
                     the Securities Act of 1933;

               (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 (a) (1) (i) and (a) (1) (ii) do
               not apply if the registration statement is on Form S-3, Form S-8
               or Form F-3, and 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 Securities
               Exchange Act of 1934 that are incorporated by reference in the
               registration statement.

          (2)  That, for the purpose of determining any liability under the
               Securities Act of 1933, 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.

     (b)  The undersigned Registrant hereby undertakes that, for purposes of
          determining any liability under the Securities Act of 1933, each
          filing of the Registrant's annual report pursuant to Section 13(a) or
          Section 15(d) of the Securities Exchange Act of 1934 (and, where
          applicable, each filing of any employee benefit plan's annual report
          pursuant to Section 15(d) of the Securities Exchange Act of 1934) 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.

     (c)  Insofar as indemnification for liabilities arising under the
          Securities Act of 1933 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 Securities and Exchange Commission such indemnification
          is against public policy as expressed in the 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
          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 Act and will be
          governed by the final adjudication of such issue.
-6-

                                  SIGNATURES

Pursuant to the requirements of the Securities Act of 1933, 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 City of Wilton, the State of Connecticut, on this 19th day of
April 2001.

                                        MERCATOR SOFTWARE, INC.

                                        By: /s/ Roy C. King
                                           ----------------------------
                                           Roy C. King
                                           President and Chief Executive Officer

                                POWER OF ATTORNEY

          EACH SUCH PERSON WHOSE SIGNATURE appears below constitutes and
appoints, jointly and severally, Roy C. King and Richard Applegate and each of
them, with full power to act without the other, his true and lawful attorney-in-
fact and agent, with the power of substitution and resubstitution, for him and
in his name, place and stead, in any and all capacities, to sign any amendments
to this Registration Statement on Form S-8 (including post-effective amendments)
and to file the same, with all exhibits thereto, and other documents in
connection therewith, with the Securities and Exchange Commission, hereby
ratifying and confirming all that said attorney-in-fact, or his or her
substitute or substitutes, may do or cause to be done by virtue hereof.

          Pursuant to the requirements of the Securities Act of 1933, this
Registration Statement has been signed by the following persons in the
capacities and on the date indicated.
Signature                                Title                                         Date
             ---------                                -----                                         ----
/s/ Roy C. King
---------------------------------     President, Chief Executive Officer                      April 19, 2001
  Roy C. King                         and Director

  /s/ Richard Applegate
---------------------------------     Vice President, Finance and                             April 19, 2001
  Richard Applegate                   Accounting and Chief Financial Officer

  /s/ James P. Schadt
---------------------------------     Chairman of the Board of Directors                      April 19, 2001
  James P. Schadt

  /s/ Diane P. Baker
---------------------------------     Director                                                April 19, 2001
  Diane P. Baker

  /s/ Constance F. Galley
---------------------------------     Director                                                April 19, 2001
  Constance F. Galley

  /s/ Ernest E. Keet
---------------------------------     Director                                                April 19, 2001
  Ernest E. Keet

  /s/ Richard Little
---------------------------------     Director                                                April 19, 2001
  Richard Little

  /s/ Dennis G. Sisco
---------------------------------     Director                                                April 19, 2001
  Dennis G. Sisco

  /s/ Mark Stevens
---------------------------------     Director                                                April 19, 2001
  Mark Stevens
INDEX TO EXHIBITS

       Exhibit                          Description of Exhibit
       -------                          ----------------------

          4.1           Amended and Restated Certificate of Incorporation, as
                        amended, of the Registrant (filed as Exhibit 3.1 to the
                        Registrant's Quarterly Report on Form  10-Q on November
                        14, 2000, File No. 000-22667 (7674707) and incorporated
                        by reference herein).*

          4.2           Amended and Restated By-Laws of the Registrant (filed
                        as Exhibit 3.1 to the Registrant's Registration
                        Statement on Form 8-A on September 4, 1998, File No.
                        000-22667 (98704715), and incorporated by reference
                        herein).*

          4.3           1997 Equity Incentive Plan, as amended, of the
                        Registrant (filed as Exhibit 4.06 to the Registrant's
                        Registration Statement on Form S-8 on October 15, 1997,
                        File No. 333-37969, and incorporated by reference
                        herein).*

          4.4           Certificate of Designation specifying the terms of the
                        Series A Junior Participating Preferred Stock of the
                        Registrant (filed as Exhibit 3.2 to the Registrant's
                        Registration Statement on Form 8-A on September 4,
                        1998, File No. 000-22667 (98704715), and incorporated
                        by reference herein).*

          4.5           Rights Agreement dated September 2, 1998 between the
                        Registrant and the Bank of New York (filed as Exhibit
                        3.3 to the Registrant's Registration Statement on Form
                        8-A on September 4, 1998, File No. 000-22667
                        (98704715), and incorporated by reference herein).*

          5.1           Opinion of Testa, Hurwitz & Thibeault, LLP.**

         23.1           Consent of Testa, Hurwitz & Thibeault, LLP (contained
                        in its opinion as Exhibit 5.1).

         23.2           Consent of KPMG, LLP.**

         24.1           Power of Attorney (included as part of the signature
                        page of this Registration Statement).

     *Not-filed herewith. In accordance with Rule 411 promulgated pursuant to
the Securities Act of 1933, as amended, reference is made to the documents
previously filed with the commission, which are incorporated by reference
herein.
     **Filed herewith.