Reissue & Reexamination

Certificate of Correction

For small mistakes — typographical or clerical errors, or errors made by the USPTO — the owner can request a Certificate of Correction. It patches the error without reopening the patent. USPTO-caused errors are corrected free; applicant errors carry a fee. This is the lightest-touch fix and does not put the rest of the patent at risk.

Reissue

When a patent is wholly or partly inoperative or invalid through error — claims drafted too narrowly (leaving competitors room) or too broadly (vulnerable to invalidity), or defects in the specification — the owner can surrender it and seek a reissue with corrected claims. A broadening reissue must be filed within two years of grant; a narrowing reissue can be filed any time. The catch: reissue reopens the entire patent to examination, so the examiner can scrutinize all claims, not just the ones you wanted to fix. It is powerful but not without risk.

Ex Parte Reexamination

Any person can ask the USPTO to re-examine an issued patent by citing prior-art patents or printed publications that raise a "substantial new question of patentability." If granted, an examiner re-examines the patent and can confirm, amend, or cancel claims. It is examination-style: if a third party files it, their involvement is minimal after the request (hence "ex parte"). It is cheaper than an IPR but gives the challenger far less control and no adversarial trial — and patent owners sometimes use it themselves to shore up a patent against known prior art before asserting it.

How these differ from IPR and PGR

Inter partes review (IPR) and post-grant review (PGR) are adversarial trials before the Patent Trial and Appeal Board, with active participation from both sides, limited discovery, and a written decision. They are the modern, powerful way for a third party to challenge a patent — and IPR has largely replaced the old inter partes reexamination.

Reexamination, by contrast, is examination-style before a single examiner with minimal third-party participation — cheaper, but with far less control for the challenger. And reissue is not a challenge at all: it is the patent owner's own tool to fix a defective patent. Choosing among them depends on who you are (owner or challenger), what you want (fix, broaden, narrow, or kill), and how much control and money you are prepared to commit.

The intervening-rights catch

When claims change through reissue or reexamination, third parties who relied on the original patent may acquire intervening rights — the right to continue what they were doing, or compensation for investments made, before the claims changed. This protects people who reasonably relied on the patent as originally granted. It is a key reason patentees weigh reissue carefully: changing your claims can limit your ability to enforce the new ones against parties who were already in the market.