In contemporary patent disputes after the passage of the America Invents Act, it is common for the same patent to be at issue in district-court litigation and in inter partes review (IPR) proceedings before the Patent Trial and Appeal Board at the same time. In principle, the PTAB and a judge or jury could reach opposite conclusions about the validity of the same patent, with the Federal Circuit resolving appeals from the litigation and the PTAB proceedings.

Anticipating this possibility, Congress enacted 35 U.S.C. §315(e)(2) as part of the AIA, estopping IPR petitioners from raising certain defenses in district court. The most common use of that estoppel provision has been to bar an unsuccessful IPR petitioner from later re-arguing in district court the same invalidity challenges that it lost before the PTAB.