Historically, inventors who assign a patent to a company or other entity have been barred from later challenging the patent’s validity under the doctrine of “assignor estoppel.” This common-law doctrine has been in place for years. However, a new Federal Circuit decision scales it back by holding that assignor estoppel cannot stop certain inter partes review (IPR) proceedings filed by inventors with the Patent Trial and Appeals Board (PTAB).

In Arista Networks v. Cisco Systems, Inc. (Fed. Cir. Nov. 9, 2018), the court considered an appeal from the PTAB decision in an IPR proceeding. In the case, a company founded by an inventor (who was a former employee of the patent holder) argued that certain claims of the patent were obvious in view of prior art. While acknowledging that assignor estoppel is a “rule well settled by 45 years of judicial consideration and conclusion,” the court found that in the America Invents Act reveals Congress’ intent for a different rule in IPR proceedings. Specifically, since 35 U.S.C. §311(a) states that any “person who is not an owner of the patent” may file an IPR petition, the court ruled that an inventor who has assigned his or her interest — and who therefore is no longer an owner of the patent — may file an IPR petition that challenges validity of the patent.

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