In a June decision, the Supreme Court in Minerva Surgical v. Hologic, 141 S. Ct. 2298 (2021), breathed new life into the doctrine of assignor estoppel, a centuries-old doctrine based in fundamental fairness principles, that limited an inventor’s or an assignor’s ability to invalidate a patent it once owned and then transferred for value. But, while the Supreme Court rejuvenated the aging doctrine, it also limited the scope of its application, permitting assignors in certain situations to challenge the validity of the assigned patent in situations where fairness principles should allow.

Background: The Assignor Estoppel Doctrine

At its core, assignor estoppel restricts an assignor from invalidating a patent it previously assigned for value. The doctrine is grounded in the basic fairness principle that a party should not be permitted to benefit by making inconsistent representations—i.e., an assignor should not be rewarded for making assurances during an assignment negotiation that a patent has some value, and yet later during patent litigation claiming that the patent is invalid and thus worthless.