1

                                                                     Exhibit 5.1

                [Letterhead of Wilson Sonsini Goodrich & Rosati]

                                August 23, 2000


Critical Path, Inc.
320 1st Street
San Francisco, California 94105

     Re:  Registration Statement on Form S-8

Ladies and Gentlemen:

     We have examined the Registration Statement on Form S-8 to be filed by you
with the Securities and Exchange Commission on or about August 24, 2000 (the
"Registration Statement"), in connection with the registration under the
Securities Act of 1933, as amended, of an aggregate of 185,316 shares of Common
Stock, par value $0.001(the "Shares"), both issued and outstanding and unissued
and reserved for issuance pursuant to the Netmosphere 1997 Stock Option Plan and
the Netmosphere 1999 Equity Incentive Plan (the "Plans"). As your legal counsel,
we have examined the proceedings taken and are familiar with the proceedings
proposed to be taken by you in connection with the sale and issuance of the
Shares under the Plans.

     It is our opinion that the Shares will be, when issued and sold in the
manner referred to in the Plans, legally and validly issued, fully paid and
nonassessable.

     We consent to the use of this opinion as an exhibit to the Registration
Statement and further consent to the use of our name wherever appearing in the
Registration Statement and any subsequent amendment thereto.

                                       Very truly yours,


                                       WILSON SONSINI GOODRICH & ROSATI
                                       Professional Corporation

                                       /s/ Wilson Sonsini Goodrich & Rosati
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