In United States patent law, 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". The Leahy-Smith America Invents Act makes substantial changes to the U.S. patent system, including new mechanisms for challenging patents at the U.S. Patent and Trademark Office. One of the new mechanisms is a post-grant review proceeding, which will provide patent challengers expanded bases on which to attack patents.
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 substantial 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 indeed raises 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 those 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.
Public notice 
The proceedings of all reexaminations are made available to the public on the USPTO’s public PAIR (Patent Application Information Retrieval) web site. Reexaminations are assigned serial numbers and cross referenced as child applications of originally issued patents.
The process of reexamination has the potential to increase the quality of patents issued and to encourage public input in the process.
Ex parte and inter partes reexaminations 
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. The fee for filing a request for an ex parte reexamination is $17,750 as of Oct. 5, 2012.
Inter partes reexaminations are initiated by members of the public, and said members of the public continue to participate in the proceedings. The fee for filing a petition to institute an inter partes review is $27,200 as of Oct. 5, 2012.
Duplicate requests for Inter partes reexaminations by the same requesting party are prohibited under 35 U.S.C. § 317.
747 requests for ex parte reexaminations were filed in FY2012 (corresponding to about 0.28% of the total number of patents issued that year), though roughly 90% of these requests were made by the patent owner. Some 640 requests for inter partes reexaminations were filed during FY2012, a figure that has been rising susbstantially every year and a fourfold increase since FY2008.
Statistics released by the USPTO for reexaminations for the period of 1981 to 2007 showed that for ex parte reexaminations, claims were changed in average 64% of the cases. In 26% of the cases, all claims are confirmed with no changes, while in 10% of the cases, all claims were invalidated. For inter partes reexaminations, claims were changed in seven of the eight cases that had been completed by the time the statistics were released.
Notable reexaminations 
NTP patents 
The NTP patents covering BlackBerry technology are currently undergoing a number of reexaminations because new prior art has been discovered which had not been considered by the patent office when the patent applications were first examined. Some of these reexaminations are inter partes, some of them are ex parte, some of them were initiated by the director. Some of the patents have had a number of reexaminations filed. These multiple reexaminations have been merged into single reexaminations, each for the patent in question.
As of April 2006, all of the NTP claims that have been acted upon have been rejected on the basis of the substantial new questions of patentability. It is yet known whether NTP will narrow its claims to get around the rejections, or succeed in an appeal.[dated info]
Method for swinging on a swing 
U.S. Patent 6,368,227 entitled "Method of swinging on a swing" was issued in 2002 to applicant Steven Olson. This patent was filed shortly after business method patents became allowable under the US patent law due to the 1998 State Street decision. The patent claimed an improved method for a child to swing on a swing.
The PTO director ordered a reexamination, and the claims were subsequently rejected. The patent owner elected not to appeal. A reexamination certificate was issued canceling all the claims.
Crustless peanut butter and jelly sandwich 
U.S. Patent 6,004,596 entitled "Sealed crustless sandwich" was issued in 1999 to applicants Len Kretchman and David Gesked. The patent claimed an improved crustless peanut butter and jelly sandwich, which could be mass produced and sold in stores.
This patent has been widely ridiculed in the media as an example of an obvious invention, which should never have been granted a patent.
The patent was licensed to Smuckers, which then introduced the Uncrustables brand of frozen no-crust sandwiches. Smuckers invested about $20 million to build a factory in Scottsville, Kentucky to produce the product. Its annual sales in 2005 were $US 60 million.
To enforce the patent, Smuckers filed a patent infringement lawsuit against alleged infringer, Albie’s Foods. Albie’s Foods responded by filing a request for ex parte reexamination.
The examiner rejected the claims in the patent, and the rejection had been appealed to the BPAI. The BPAI rejected the claims, and the USPTO issued a notice that it intends to cancel all of the claims.
See also 
- Interference proceeding (U.S. patent law)
- Opposition procedure before the European Patent Office
- Scire facias
- Sterne, Kessler, Goldstein & Fox P.L.L.C. (September 8, 2011). "10 Things To Know About Post-Grant Review Under The America Invents Act of 2011". The National Law Review. Retrieved September 10, 2012.
- USPTO’s public PAIR (Patent Application Information Retrieval)
- "PUBPAT provides comments to USPTO on inter partes reexamination and rules governing practitioners: Argues All Patents Should be Subject to Adversarial Post Grant Review and All Patent Attorneys Should Have Continuing Education Requirements". Public Patent Foundation. February 23, 2007. Retrieved 2 October 2010.
- USPTO Ex parte and Inter partes reexamination fee schedule
- 35 U.S.C. § 317, found at Inter partes reexamination prohibited at Bitlaw.com website. Accessed July 3, 2008.
- USPTO FY2012 Performance and Accountability Report, Tables 14A and 6
- USPTO FY2012 Performance and Accountability Report, Table 14B
- Robert A. Saltzberg and Mehran Arjomand, Reexaminations Increase in Popularity, Morrison and Foerster, September 2007
- "Uncrustables". smuckers.com. Retrieved 2 October 2010. Uncrustables sandwiches, The J.M. Smucker Co., retrieved on June 16, 2006.
- The J. M. Smucker Company Announces Fourth Quarter and Full-Year Results, The J. M. Smucker Company, News Release, June 16, 2005, retrieved on www.corporate-ir.net on June 16, 2006