Exhibit 5.1
                                                                     -----------

                                                  July 2, 2001

Insightful  Corporation
1700 Westlake Avenue North, Suite 500
Seattle,  WA  98109-3044

     RE:  Registration  statement  on Form S-8 Relating to the 2001 Stock Option
          and Incentive Plan, the 2001 Employee Stock Purchase Plan and the 2001
          Non-Employee  Director  Stock  Option  Plan  (the  "Plans")

Dear  Sir  or  Madam:

     Reference is made to the above-captioned registration statement on Form S-8
(the  "Registration  Statement") filed by Insightful Corporation (the "Company")
on  the  date  hereof  with  the  Securities  and  Exchange Commission under the
Securities  Act  of 1933, as amended, relating to an aggregate of 823,000 shares
of  Common  Stock, $.01 par value, of the Company issuable pursuant to the Plans
(the  "Shares").

     We  have examined, are familiar with, and have relied as to factual matters
solely  upon,  copies  of  the  Plans,  the  Amended and Restated Certificate of
Incorporation  and Amended and Restated By-Laws of the Company, the minute books
and  stock  records  of  the  Company  and  originals  of  such other documents,
certificates  and  proceedings  as  we  have deemed necessary for the purpose of
rendering  this  opinion.

     Based  on  the  foregoing,  we are of the opinion that the Shares have been
duly  authorized  and,  when issued and paid for in accordance with the terms of
the  Plans,  will  be  validly  issued,  fully  paid  and  nonassessable.

     We  hereby  consent  to  the  filing  of this opinion as Exhibit 5.1 to the
Registration  Statement.

                                            Very  truly  yours,

                                            TESTA, HURWITZ & THIBEAULT, LLP