Reexamination

1. RequestAny person may file a written request, accompanied by the reexamination fee, on the basis of prior art cited under 35 U.S.C. 301¹. That prior art consists of patents or printed publications⁷. The request must set forth the pertinency and manner of applying the cited prior art to every claim for which reexamination is requested¹. Under 37 CFR 1.510 it must also point out each substantial new question of patentability and include a copy of every patent or printed publication relied on¹⁰. A third party requester must certify that the statutory estoppel provisions of 35 U.S.C. 315(e)(1) or 325(e)(1) do not prohibit the request¹⁰.
2. DeterminationWithin three months after the request is filed, the Director determines whether it raises a substantial new question of patentability affecting any claim². Such a question can exist even though a patent or printed publication was previously cited to or considered by the Office².
3. Order and statementsIf a substantial new question is found, the determination includes an order for reexamination³. The patent owner is given a reasonable period, not less than two months, to file a statement, including any amendment or new claims. The requester may file a reply within two months from the date the statement is served³.
4. ReexaminationAfter those periods expire, reexamination is conducted under the procedures for initial examination in 35 U.S.C. 132 and 133, with special dispatch¹¹. The patent owner may propose amendments and new claims, but no claim that enlarges the scope of a claim of the patent is permitted¹¹.
5. AppealThe patent owner may appeal under 35 U.S.C. 134 and seek court review under sections 141 to 144 with respect to any decision adverse to the patentability of an original, amended or new claim¹².
6. CertificateWhen the time for appeal has expired or any appeal has terminated, the Director issues and publishes a certificate canceling claims finally determined to be unpatentable, confirming claims determined to be patentable and incorporating any amended or new claims determined to be patentable¹³.

• Patents and printed publications only. In an ex parte reexamination ordered under 35 U.S.C. 304, the prior art considered is limited to prior art patents or printed publications applied under 35 U.S.C. 102 and 103⁴. Rejections will not be based on other matters such as public use or sale, inventorship or 35 U.S.C. 101⁵.
• Section 112 only for changes. Issues under 35 U.S.C. 112 are addressed only for new claims or amended subject matter⁵.
• Other issues are not resolved. If issues outside those limits are raised, the examiner notes them, and the patent owner may consider filing a reissue application to have them resolved⁵.
• Supplemental examination is different. For an ex parte reexamination ordered as a result of supplemental examination under 35 U.S.C. 257, the prior art considered is not limited to patents and printed publications^4,5.
• Repeated art. In deciding whether to order a proceeding under chapter 30 of title 35 (35 U.S.C. 301 to 307, which includes reexamination), the Director may take into account, and reject the request because, the same or substantially the same prior art or arguments were previously presented to the Office (35 U.S.C. 325(d))^11,14.

Under 37 CFR 1.510(a), any person may file a request at any time during the period of enforceability of the patent¹⁰. The USPTO says that period is generally determined by adding 6 years to the date on which the patent expires, and that it may be extended if there is pending litigation¹⁵.

• Estoppel after IPR or PGR. A request may not be filed where 35 U.S.C. 315(e)(1) or 325(e)(1) prohibits it¹⁰. After a post-grant review that results in a final written decision, the petitioner, or its real party in interest or privy, may not request or maintain a proceeding before the Office on a claim on any ground it raised or reasonably could have raised in that review (35 U.S.C. 325(e)(1))¹⁴. See Inter partes review for the IPR counterpart.
• USPTO alert of February 6, 2026. If at least one claim of the patent was previously challenged in an IPR or PGR that resulted in a final written decision on that claim, a party submitting an anonymous reexamination request should state that the real party in interest is not the earlier petitioner, or its real party in interest or privy¹⁶.
• Proposed rule published July 22, 2026. The USPTO proposed to require a third party request for ex parte reexamination to include a statement identifying all real parties in interest, kept confidential on request. Comments were due by August 21, 2026¹⁷. As of the review date no final rule had been published, so check the USPTO's pages for what applies on the date you file.