Recent decisions by the Court of Appeals for the Federal Circuit have addressed the scope of the estoppel provision that applies to petitioners for inter parties review of issued U.S. patents, codified as §315(e) of the patent statute. In the event of a petition that results in a final written decision by the Patent Trial and Appeal Board, petitioners are estopped from requesting or maintaining another challenge to the validity of the patent in the Patent Office, or asserting invalidity in infringement litigation, in each case with respect to patent claims challenged in the IPR and any ground for invalidity that the petitioner “raised or reasonably could have raised during” the IPR. These developments should be taken into account by potential petitioners.