The Supreme Court held oral arguments for Oil States v. Greene’s Energy Services on November 27, exploring the constitutionality of inter partes review (IPR) under Article III of the US Constitution. During their questioning of counsel for the two parties and the US Government, the justices pushed for a clear-cut articulation for how, if at all, IPR might be invalidated without affecting the USPTO’s far less controversial ex parte and inter partes reexamination systems along with myriad other agency review proceedings. The justices also pressed the parties on the core issue of whether patents are private or public rights, a distinction that received particular attention from Justice Neil Gorsuch, and thus whether their invalidation can be addressed only in an Article III court. Chief Justice John Roberts emphasized the issues of due process and the applicability of the Takings Clause, while the Court’s liberal and moderate justices seemed to favor the view that, in key respects, IPR is closer to a reexamination than a trial.