**Exhibit 31.1**

**CERTIFICATIONPURSUANT TO RULE 13A-14(a) OR 15D-14(a) OF THE SECURITIESEXCHANGE ACT OF 1934, AS ADOPTED PURSUANT TO SECTION 302 OF THESARBANES-OXLEY ACT OF 2002**

I, Robert K.Weiler, certify that:

1.    I have reviewed thisquarterly report on Form 10-Q of Phase Forward Incorporated;

2.    Basedon my knowledge, this report does not contain any untrue statement of amaterial fact or omit to state a material fact necessary to make the statementsmade, in light of the circumstances under which such statements were made, notmisleading with respect to the period covered by this report;

3.    Basedon my knowledge, the financial statements, and other financial informationincluded in this report, fairly present in all material respects the financialcondition, results of operations and cash flows of the registrant as of, andfor, the periods presented in this report;

4.    Theregistrant’s other certifying officer and I are responsible for establishingand maintaining disclosure controls and procedures (as defined in Exchange Act Rules 13a-15(e) and15d-15(e)) and internal control over financial reporting (as defined inExchange Act Rules 13a-15(f) and 15d-15(f)) for theregistrant and have:

A.                Designed suchdisclosure controls and procedures, or caused such disclosure controls andprocedures to be designed under our supervision, to ensure that materialinformation relating to the registrant, including its consolidatedsubsidiaries, is made known to us by others within those entities, particularlyduring the period in which this report is being prepared;

B.                  Designed suchinternal control over financial reporting, or caused such internal control overfinancial reporting to be designed under our supervision, to provide reasonableassurance regarding the reliability of financial reporting and the preparationof financial statements for external purposes in accordance with generallyaccepted accounting principles;

C.                  Evaluated theeffectiveness of the registrant’s disclosure controls and procedures and presentedin this report our conclusions about the effectiveness of the disclosurecontrols and procedures, as of the end of the period covered by this reportbased on such evaluation; and

D.                 Disclosed in thisreport any change in the registrant’s internal control over financial reportingthat occurred during the registrant’s most recent fiscal quarter (theregistrant’s fourth fiscal quarter in the case of an annual report) that hasmaterially affected, or is reasonably likely to materially affect, the registrant’sinternal control over financial reporting; and

5.    The registrant’s other certifyingofficer and I have disclosed, based on our most recent evaluation of internalcontrol over financial reporting, to the registrant’s auditors and the auditcommittee of registrant’s board of directors (or persons performing theequivalent functions):

A.                All significantdeficiencies and material weaknesses in the design or operation of internalcontrol over financial reporting which are reasonably likely to adversely affectthe registrant’s ability to record, process, summarize and report financialinformation; and

B.                  Any fraud,whether or not material, that involves management or other employees who have asignificant role in the registrant’s internal control over financial reporting.

Date:  May 9, 2006
|        | By:    | /s/ Robert K. Weiler                      |   |
|--------|--------|-------------------------------------------|--------|
|   |   | Robert K. Weiler  Chief Executive Officer |   |

 

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