Patent ownership rights in the U.S. originate with the patent's inventors. For an entity other than the inventors to obtain those rights, it is critical to ensure that inventors have effectively assigned the rights in the invention to the entity. This also applies when a company is acquiring a patent that was previously assigned to another company. Within the last year, there have been several cases impacting assignment rights that practitioners need to be aware of.

On June 29, 2021, in Hologic v. Minerva Surgical, 141 S.Ct. 1068, the Supreme Court ruled on a case addressing assignor estoppel. Assignor estoppel is a doctrine that broadly holds that a party that has assigned a patent cannot later challenge the validity of that patent's claims. In Hologic, an assignee added an allegedly broader claim during prosecution of an acquired patent application. The court held that assignor estoppel would not apply to claims during post-assignment prosecution if such claims are materially broader than those present in the assigned patent application. The court remanded the case to the United States Court of Appeals for the Federal Circuit ("CAFC")  to determine whether the added claims were materially broader than those originally assigned. If so assignor estoppel should not apply.