The joint defense doctrine (now more frequently called the common interest doctrine) provides an exception to the normal attorney-client privilege waiver rules — allowing disclosure to others sharing an identical legal interest without triggering a waiver. Many lawyers spend hours carefully drafting written joint defense/common interest agreements.
In HSH Nordbank AG New York Branch v. Swerdlow, No. 08 Civ. 6131 (GEL), 2009 U.S. Dist. LEXIS 63711 (S.D.N.Y. July 24, 2009), Judge Gerard Lynch dealt with such a common interest agreement among plaintiffs. Among other things, Judge Lynch labeled as “wholly unpersuasive” defendants’ argument that the communications at issue did not deserve protection because the common interest participants “did not enter into a written common interest agreement until well after the communications occurred.” Id. at *18 n.12. He cited the generally accepted rule “that although the common interest doctrine applies only where a party has demonstrated the existence of an agreement to pursue a common legal strategy, the agreement need not be in writing.” Id.
Although articulating a common interest agreement in writing usually makes sense (because it allows the participants to more carefully define their rights and responsibilities), most courts do not require written agreements.