35 U.S.C. · Part III · Chapter 31, Inter partes review

35 U.S.C. 311: Inter partes review

In plain English

Inter partes review (IPR) is a trial at the Patent Trial and Appeal Board in which anyone other than the patent owner can challenge the claims of an issued patent. The grounds are limited to anticipation and obviousness under sections 102 and 103, and only on the basis of prior art consisting of patents and printed publications. Public use, on-sale activity, eligibility and section 112 issues cannot be raised in an IPR.

For patents granted under the AIA first-inventor-to-file rules, a petition can be filed only after the later of 9 months from grant or the end of any post-grant review (section 311(c)). For pre-AIA patents, it can be filed at any time after grant (37 CFR 42.102). A petition is barred if it is filed more than 1 year after the petitioner, its real party in interest or a privy was served with a complaint for infringement of the patent (section 315(b)), or if the petitioner first filed a civil action challenging validity (section 315(a)).

The Director decides whether to institute. The petition must show a reasonable likelihood that the petitioner would prevail on at least one challenged claim (section 314(a)), and institution is discretionary even when that threshold is met. Once instituted, the Board must issue a final written decision within 1 year, extendable by up to 6 months for good cause. Unpatentability is proved by a preponderance of the evidence, and claims are construed as they would be in court (37 CFR 42.100(b)). A petitioner who receives a final written decision is estopped from raising, at the USPTO or in court, any ground it raised or reasonably could have raised in the IPR (section 315(e)).

Annotation by Raj Sutariya, Co-founder, PatentAssist.ai. General information, not legal advice; the statute below governs.

AIA and pre-AIA

IPR was created by the AIA and has been available since September 16, 2012 for patents issued before, on or after that date. It replaced inter partes reexamination. Ex parte reexamination under section 302 still exists and can be requested by anyone, including the patent owner, on the basis of patents and printed publications.

Text of 35 U.S.C. 311

Current text, quoted from the official United States Code.

(a) In General.— Subject to the provisions of this chapter, a person who is not the owner of a patent may file with the Office a petition to institute an inter partes review of the patent. The Director shall establish, by regulation, fees to be paid by the person requesting the review, in such amounts as the Director determines to be reasonable, considering the aggregate costs of the review.
(b) Scope.— A petitioner in an inter partes review may request to cancel as unpatentable 1 or more claims of a patent only on a ground that could be raised under section 102 or 103 and only on the basis of prior art consisting of patents or printed publications.
(c) Filing Deadline.— A petition for inter partes review shall be filed after the later of either—
(1) the date that is 9 months after the grant of a patent; or
(2) if a post-grant review is instituted under chapter 32, the date of the termination of such post-grant review.

Key cases

Cuozzo Speed Technologies, LLC v. Lee, 579 U.S. 261 (2016). Section 314(d) bars judicial review of the decision to institute an IPR where the challenge is grounded in the statutes closely related to that decision.
Oil States Energy Services, LLC v. Greene's Energy Group, LLC, 584 U.S. 325 (2018). IPR does not violate Article III or the Seventh Amendment. Granting a patent is a matter of public rights, and the USPTO may reconsider that grant.
SAS Institute Inc. v. Iancu, 584 U.S. 357 (2018). When the USPTO institutes an IPR, it must decide the patentability of every claim the petitioner challenged, not only some of them.
Thryv, Inc. v. Click-To-Call Technologies, LP, 590 U.S. 45 (2020). The Board's decision that a petition is not time-barred under section 315(b) is part of the institution decision and cannot be appealed.
United States v. Arthrex, Inc., 594 U.S. 1 (2021). Administrative patent judges cannot issue final, unreviewable decisions. The Director must be able to review final written decisions, which led to the USPTO's Director Review process.

Practical notes

Institution practice has changed. Under a March 26, 2025 USPTO memorandum on interim processes for PTAB workload management, institution decisions are split: the Director decides discretionary considerations, on separate briefs from each side, and a Board panel considers the merits. Discretionary factors include parallel litigation, whether validity has already been adjudicated, how long the claims have been in force and the strength of the challenge. Check the PTAB's Director Institution page for the current process before filing or opposing a petition.

At the time of writing the fees are $23,750 to request review of up to 20 claims plus a $28,125 post-institution fee, with more for each claim over 20 (37 CFR 42.15(a)). There are no small entity reductions.

Estoppel is the main strategic cost for a petitioner. Put the strongest patents and printed publications in the petition, because art that could reasonably have been found in a diligent search will be hard to use later in court.

Related rules and guidance

37 CFR: § 42.15, § 42.100, § 42.101, § 42.102, § 42.104, § 42.107, § 42.108, § 42.120
MPEP: Not covered by the MPEP. PTAB trials follow 37 CFR part 42 and the PTAB's Consolidated Trial Practice Guide.