Gerson Zweifach has tried antitrust, securities, libel, and complex commercial cases to juries and courts across the United States. Over 26 years at Williams & Connolly LLP, Mr. Zweifach's litigation practice has extended across a wide variety of substantive areas, as both plaintiff’s and defendant’s counsel, with a constant focus on trial work.

In the securities field, Mr. Zweifach has represented both plaintiffs and defendants in a wide variety of actions, including the successful defense at a jury trial of an issuer sued for allegedly imposing unauthorized trading restrictions on the company's shares. Mr. Zweifach has also been called upon to defend Big 4 accounting firms as well as major law firms in securities and malpractice litigation and before the Securities and Exchange Commission.

In the antitrust field, Mr. Zweifach has successfully defended monopolization, tying, and patent antitrust actions brought in federal courts across the country, and has successfully defended clients before the Federal Trade Commission.

Mr. Zweifach’s recent matters have included the representation of Richard A. Grasso in Spitzer v. Grasso in the New York state courts, as well as the representation of Medimmune in its challenge to Genentech’s Cabilly patent in federal court in Los Angeles.  He is listed in the Best Lawyers in America (2005-07); Chambers USA Guide (2005-07); Lawdragon 500 (2007-08); and The Legal 500 – United States (2008).

He is a member of the firm's Executive Committee.