In United States patent law, a reexamination is a process whereby anyone—third party or inventor—can have a U.S. 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, in the form of patents or printed publications, 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. Process A request for a reexamination can be filed by anyone at any time during the period of enforceability of a patent. To request a reexamination, one must submit a "request for reexamination" which includes (1) a statement pointing out each "substantial new question of patentability based on prior patents and printed publications; (2) an identification and explanation for every claim for which reexamination is requested; (3) a copy of every patent or printed publication relied upon; (4) a copy of the entire patent at issue; (5) a certification that a copy of the request for reexamination has been served on the patent owner if the requester is not the patent owner; and (6) a certification by the third-party requester that the statutory estoppel provisions of 35 U.S.C. 351(e)(1) or 35 U.S.C. 325(e)(1) do not prohibit the requester from filing the request for reexamination. 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