Assignor Estoppel Does Not Apply To IPRs

Assignor estoppel is a long-established, common-law doctrine of equity, which prevents a party who assigns a patent to another from later challenging the validity of the assigned patent.  The doctrine also applies to parties in privity with an estopped assignor, such as a corporation founded by the assignor.  On November 9 however, the Federal Circuit (the "Court") handed down a decision in Arista Networks, Inc. v. Cisco Sys., Inc., 17-1525, which says that assignor estoppel does not apply to Inter Parte Review (IPR) proceedings.

Arista petitioned for an IPR of certain claims of a U.S. Patent No. 7,340,597 owned by Cisco. The named inventor is Dr. David Cheriton, who at the time of the invention was employed by Cisco as a technical advisor and chief product architect.  Dr. Cheriton assigned his entire right, title and interest in his invention to Cisco, and shortly thereafter, left Cisco to co-found Arista.  Dr. Cheriton once served as a director of Arista and was