An ex parte reexamination is a patent office procedure where the inventor of a patent or a third party can request that a patent be reexamined by a patent examiner to verify that the subject matter of the patent claims is patentable.  The threshold standard for initiating an ex parte reexamination is to show that the prior art subject to the ex parte reexamination raises a “substantial new question of patentability” as to at least one claim in the request.

An ex parte reexamination can be filed at any time during the enforceability of a patent (including after expiration).  Ex parte reexaminations are often filed by defendants that are sued for patent infringement or by patent owners who desire to confirm claims in light of new prior art or amend claims to preserve their validity over new prior art.

Third parties (parties other than the patent owner) who initiate ex parte reexamination proceedings generally do not participate in the proceeding after the examination is instituted.

The reexamination process is similar to the examination process of a newly-filed patent application.  The examiner will review the claims in light of the prior art submitted in connection with the reexamination proceeding.  Patent owners may file statements addressing the new questions of patentability at issue in the proceeding.  Patent owners may also make amendments to the claims subject to reexamination.

The examiner will either confirm the claims as filed or amended by issuing a reexamination certificate, or may reject the claims.  The patent owner may appeal any rejected claims to the Board of Patent Appeals and Interferences at the United States Patent and Trademark Office.  If the decision from the Board of Patent Appeals and Interferences is adverse, the patent owner may file an appeal to the Court of Appeals for the Federal Circuit.

Legal estoppel does not attach to parties who initiate ex parte reexaminations against the patent owner.

Ex parte reexaminations have been available since 1981 and are codified at 35 U.S.C. § 302.  Regulations regarding ex parte reexaminations are set forth at 37 C.F.R. § 1.510.

The America Invents Act (AIA) was signed into law on September 16, 2011. The AIA did little to change the ex parte reexamination process.  However, the AIA added new post grant procedures that gave parties challenging patents more options, including Inter Partes Review, Post-Grant Review, and the Covered Business Method Patent Review proceedings.