Exhibit 8.1

                   CADWALADER, WICKERSHAM & TAFT LETTERHEAD

                                        February 12, 2001

Vialog Corporation
32 Crosby Drive
Bedford, MA 01730

Ladies and Gentlemen:

     You have requested our opinion regarding the material U.S. federal income
tax consequences set forth under the headings "The Merger - Tax Treatment" and
"Material Tax Considerations - U.S. Federal Income Tax Consequences" in the
Proxy Statement/ Prospectus (the "Proxy Statement/ Prospectus") which will be
included in the Registration Statement on Form F-4 (the "Registration
Statement") filed by Genesys SA on the date hereof with the Securities and
Exchange Commission (the "Commission") under the Securities Act of 1933, as
amended (the "Act"). The Proxy Statement/ Prospectus relates to the proposed
merger of ABCD Merger Corp., a Massachusetts corporation and a direct
wholly-owned subsidiary of Genesys SA, a corporation (societe anonyme) organized
under the laws of France, with and into Vialog Corporation, a Massachusetts
corporation, pursuant to an Agreement and Plan of Merger dated as of October 1,
2000 (the "Merger Agreement"). All capitalized terms used but not defined herein
shall have the meaning ascribed to such terms in the Merger Agreement. This
opinion is delivered in accordance with the requirements of Item 601(b)(8) of
Regulation S-K under the Securities Act.

     We have reviewed the Proxy Statement/ Prospectus and such other materials
as we have deemed necessary or appropriate as a basis for our opinion described
therein, and have considered the applicable provisions of the Internal Revenue
Code of 1986, as amended, Treasury regulations promulgated thereunder, pertinent
judicial authorities,


interpretive rulings of the Internal Revenue Service and such other authorities
as we have considered relevant all as in effect on the date hereof. It should be
noted that statutes, regulations, judicial decisions and administrative
interpretations are subject to change at any time and, in some circumstances,
with retroactive effect. A change in the authorities upon which our opinion is
based could affect our conclusions.

     Based upon the foregoing, the statements made under the headings "The
Merger - Tax Treatment" and "Material Tax Considerations - U.S. Federal Income
Tax Consequences" in the Proxy Statement/ Prospectus, set forth our opinion on
the law. There can be no assurance that contrary positions may not be asserted
by the Internal Revenue Service.

     In accordance with the requirements of Item 601(b)(23) of Regulation S-K
under the Securities Act, we hereby consent to the use of our name under the
headings "The Merger - Tax Treatment" and "Material Tax Considerations - U.S.
Federal Income Tax Consequences" in the Proxy Statement/ Prospectus and to the
filing of this opinion as an Exhibit to the Registration Statement. In giving
this consent, we do not thereby admit that we are within the category of persons
whose consent is required under Section 7 of the Act or General Rules and
Regulations of the Commission.

                               Very truly yours,

                       /s/ CADWALADER, WICKERSHAM & TAFT