SAS Institute, Inc. (SAS) (plaintiff) sought an inter partes review of a software patent owned by ComplementSoft. SAS alleged that all 13 of the patent’s claims were unpatentable. The Patent Trial and Appeal Board (the board) (defendant) instituted review on only some claims and denied review on the rest. The board argued that it had the authority to conduct a partial review based on a regulation enacted by the Patent Office. The board claimed that although it may have had to decide every claim challenged by SAS, the board was not required to bring every claim into the review process. The board argued that because the statutory language required it to evaluate claims individually, it was also entitled to institute review on a claim-by-claim basis. SAS sought review in the Federal Circuit, arguing that 35 U.S.C. § 318(a) required the board to decide the patentability of every claim SAS challenged in its petition. The Federal Circuit rejected SAS’s argument. The Supreme Court granted certiorari.