The common interest doctrine allows separately represented clients to exchange privileged communications without waiving the privilege. However, the doctrine applies only to communications involving the participants’ common legal interests.
Courts’ application of the common interest doctrine in the patent context highlights the doctrine’s subtlety. Several courts have held that the buyer and seller of a patent can share a sufficiently common interest in the patent’s validity. In that circumstance, the common interest doctrine can protect their communications about that patent’s validity. However, in Mondis Technology, Ltd. v. LG Electronics, Inc., Civ. A. No. 2:07-CV-565-TJW-CE c/w 2:08-CV-478-TJW, 2011 U.S. Dist. LEXIS 47807 (E.D. Tex. May 4, 2011), the court rejected a patent buyer’s claim that the common interest doctrine protected some of its communications with the seller – involving the purchase price. As the court explained, “[a]lthough [buyer] correctly argues it had a common legal interest with [seller] that the patents remain valid, the core of the communications was not the validity of the patents but instead a negotiation for potential adjustment to the contract price of the patent sale.” Id. at *20. The court thus found that the buyer had waived privilege protection for communications about the purchase price by disclosing those communications to the seller.
Applying the common interest doctrine often requires a communication-by-communication analysis.