A reexamination is a process whereby a third party or inventor can have a patent reexamined by a patent examiner to verify that the subject matter it claims is patentable. To have a patent reexamined, an interested party must submit prior art that raises a “substantial new question of patentability”.

A request for a reexamination can be filed by anyone at anytime during the period of enforceability of a patent. To request a reexamination, one must submit a “request for reexamination,” pay a fee, and provide an explanation of the new reasons why the patent is invalid based on prior art. Copies of the prior art must be provided, and the party making the request has to let the owner of the patent know that a request has been filed. If the USPTO finds that the request does raise a substantial new question of patentability, the USPTO orders a reexamination.

Requests for reexamination are often filed by third parties, who are already involved in an infringement lawsuit concerning the patent at issue. By filing for a reexamination, such parties seek to invalidate the patent while keeping legal fees low. If the judge agrees, the trial proceedings may be put on hold pending the outcome of the reexamination.

Inventors themselves also file requests for reexamination. Such requests may be filed before the inventors sue another party for infringing the patent, to make sure that the patent is valid in light of any prior art they may have discovered since the issuance of the patent.

The patent office itself may initiate “director initiated” reexaminations, for example, when there is reason to question the validity of the patent. The director, for example, ordered reexaminations of the NTP, Inc. patents which covered BlackBerry mobile e-mail technology.

Once a reexamination is ordered, a new examiner is assigned to the case, and the patent goes through another examination similar to the examination it received the first time around. If any claims are rejected in light of the new questions raised, then the patent owner can narrow or cancel the said claims. The patent owner can also submit new claims, provided they are not broader than the claims in the original patent. If the examiner makes a rejection “final”, the patent owner can appeal the decision to the Board of Patent Appeals and Interferences (BPAI) at the USPTO. The patent owner can file an appeal to the Court of Appeals for the Federal Circuit and even to the US Supreme Court, if permitted.

Once the reexamination has been concluded, a “certificate of reexamination” is issued. The certificate makes any corrections to a patent as are required under the reexamination. If all the claims in the patent are rejected, the patent gets nullified.

The process of reexamination has the potential to increase the quality of patents issued and to encourage public input in the process.

Ex parte reexaminations are initiated by members of the public, but once said members submit their request, they no longer actively participate in the proceedings. The correspondence is strictly between the examiner and the patent owner.

Inter partes reexaminations are initiated by member of the public, but said members of the public continue to participate in the proceedings.

About 500 requests for ex parte reexaminations are filed every year. The number corresponds to about 0.33% of the number of patents issued in a given year. About 60 requests for inter partes reexaminations are filed per year.

About 64% of the patents in an ex parte reexamination have some of their claims not rejected. In 26% of the cases, all claims are confirmed. In other words, a patent is completely invalidated in only 10% of all ex parte reexaminations.