When a patent or patent family is subject to multiple validity challenges, a petitioner in an inter partes review may seek to assert collateral estoppel to preclude relitigation of issues decided in a previous proceeding. Collateral estoppel, which is also called issue preclusion, is appropriate where: “(1) the issue is identical to one decided in the first action; (2) the issue was actually litigated in the first action; (3) resolution of the issue was essential to a final judgment in the first action; and (4) [the party against whom issue preclusion is asserted] had a full and fair opportunity to litigate the issue in the first action.” In re Freeman, 30 F.3d 1459, 1465 (Fed. Cir. 1994). Collateral estoppel is “premised on principles of fairness,” which leaves considerable latitude to the PTAB in deciding whether to apply the doctrine. Continue reading “Collateral Estoppel in an IPR”