What Is an Inter Partes Review?

Inter partes review (IPR) is a trial at the Patent Trial and Appeal Board (PTAB) in which a petitioner asks the Patent Office to cancel patent claims as anticipated or obvious over earlier patents and printed publications (35 U.S.C. §§ 311-319). It is available after nine months from grant, and a petitioner sued for infringement must file within one year after being served with the complaint (§§ 311(c), 315(b)). The only grounds are anticipation and obviousness based on patents and printed publications (§ 311(b)), and the Board decides by a preponderance of the evidence (§ 316(e)).

The proceeding runs from petition, to the patent owner's preliminary response, to institution, to trial before a three-judge panel, to a final written decision due within one year after institution, extendable by six months for good cause (§ 316(a)(11)). The petitioner must show a reasonable likelihood of prevailing on at least one claim for review to be instituted (§ 314(a)), but the Office may deny review even if that standard is met. Institution decisions are final and nonappealable (§ 314(d)). Either party may appeal a final written decision to the Federal Circuit (§ 319), and a petitioner that reaches a final written decision is estopped from raising in court a patent-or-publication ground it raised or reasonably could have raised (§ 315(e)).

Since 2025, the Patent Office has denied many petitions on discretionary grounds, including parallel litigation and the age of the patent, and effective October 20, 2025, the Director decides whether to institute every IPR and post-grant review. Watch item only, per the PTAB guide: in October 2025 the Patent Office proposed rules (90 Fed. Reg. 48335) that would further restrict review (RIN 0651-AD89); a final rule was sent to the Office of Information and Regulatory Affairs on July 22, 2026, and as of the guide's update had not been published. Anyone sued on a patent should plan for the possibility that review will not be available.

This term also appears as a short entry in the 36-term patent glossary in "Patent Basics for Litigation, with a Glossary." This page is the fuller treatment and links to that guide.

Pinpoint: 35 U.S.C. §§ 311-319. Related term: Inter Partes Review.

Sources.

• 35 U.S.C. § 311: inter partes review. law.cornell.edu
• 35 U.S.C. § 314: institution of inter partes review. law.cornell.edu

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