What is the difference between a reissue and a reexamination?

A reissue and a reexamination are both post-grant USPTO procedures that affect an issued patent, but they serve fundamentally different purposes and are available to different parties. Reissue is a patent owner's tool to correct errors in the patent itself. Reexamination is a prior-art validity challenge that any party can request.

Reissue: correcting errors in the patent

A reissue application is available when a patent is, through error, deemed wholly or partly inoperative or invalid, due to a defective specification or drawing, or because the patentee claimed more or less than they were entitled to in the original patent. The statutory basis is 35 U.S.C. § 251.

Only the patent owner (or assignee of the entire interest) may file a reissue application; a third party has no ability to initiate one. The owner must surrender the original patent to obtain the reissued patent.

Correctable errors under § 251 include:

• Defects in the specification or drawings
• Claims written too narrowly (leaving valuable scope unprotected) or too broadly (claiming more than the patentee was entitled to)

A reissue application may not introduce new matter. Everything added must find support in the original disclosure. The reissued patent covers only the unexpired portion of the original patent term, so reissue cannot extend exclusivity.

A reissue application must include an oath or declaration specifically identifying at least one error relied upon as the basis for reissue.

Broadening claims after grant

Reissue is the only post-grant USPTO mechanism that permits an owner to broaden the scope of issued claims. That option is available only if the reissue application is filed within a limited post-grant window; after that window closes, only narrowing or corrective reissues remain available. Practitioners who realize issued claims are too narrow should evaluate a broadening reissue promptly after the patent grants.

Reexamination: a prior-art challenge to validity

Ex parte reexamination is a mechanism for challenging the validity of issued patent claims based on prior art patents and printed publications. Any person may, at any time during the period of enforceability of a patent, file a request for ex parte reexamination. This includes competitors, licensees, accused infringers, and the patent owner itself.

A reexamination request must be based on prior art patents and printed publications; no other grounds are proper as the basis for the request. The USPTO must find that the request raises a substantial new question of patentability before ordering the proceeding.

Unlike reissue, reexamination cannot correct errors in the specification or drawings; its scope is limited to patentability challenges based on prior art.

During reexamination, the patent owner may propose claim amendments, but no amended or new claim may enlarge the scope of any existing claim. Only narrowing changes are permitted. Reexamination proceedings must be conducted with special dispatch within the USPTO.

At conclusion, the USPTO issues a reexamination certificate that cancels claims found unpatentable, confirms claims found patentable, and incorporates any new or amended claims determined to be patentable.

In ex parte reexamination, the third-party requester has very limited participation after the initial filing. The patent owner responds to office actions largely without the requester's further involvement, making the proceeding effectively one-sided once the order issues.

A note on inter partes review

The America Invents Act also established inter partes review (IPR) before the Patent Trial and Appeal Board, a related but distinct proceeding. A person who is not the patent owner may petition to institute an inter partes review, challenging claims on novelty or obviousness grounds based on prior art patents or printed publications. The choice between IPR and ex parte reexamination turns on strategic factors including timing, estoppel risk, petitioner participation rights, and the depth of adversarial engagement each proceeding offers.

Side-by-side comparison

Intervening rights

Both procedures trigger intervening rights protections for third parties who relied on the original patent's scope before changes took effect.

For reissue: anyone who, prior to the grant of a reissue, made, purchased, offered to sell, or used the patented thing may continue those activities unless doing so would infringe a valid claim of the reissued patent that was also present in the original patent.

For reexamination: amended or new claims incorporated through a reexamination certificate carry the same intervening rights effect. Third parties who practiced the claimed subject matter before the certificate issued, under claims that did not previously exist, may have a defense for pre-certificate activities.

When to use which

Choose reissue when the problem is the patent owner's error in the patent itself: claims that are too narrow or too broad, a defective specification, or a missed priority claim. The owner controls the proceeding and can address errors beyond prior art.

Choose reexamination (or IPR) when the goal is to challenge whether the claims should have been granted in the first place, based on prior art the examiner may have missed. Any party can request it, but amendments are limited to narrowing changes and the grounds are restricted to prior art patents and printed publications.