David I. Berl and Christopher A. Suarez write: The estoppel provision of the America Invents Act, 35 U.S.C. 315(e), was touted originally as a check against patent challengers using inter partes review (“IPR”) proceedings to attack patents serially on the same or similar grounds. That provision precludes an IPR petitioner, or the real party in interest or privy of the petitioner, from asserting invalidity challenges in subsequent IPR, district court, or International Trade Commission (“ITC”) proceedings “on any ground that the petitioner raised or reasonably could have raised during” an IPR that resulted “in a final written decision.” Given the frequency of IPR and associated district court challenges, the scope of the AIA’s estoppel provision, with respect to the parties and arguments it estops, has become and will continue to be a critical and frequently contested issue for litigants.