The statute governing reexamination was amended in 1999 and 2002 to create a right for inter parties reexamination. Basically, the party bringing the request for reexamination is allowed to participate more fully in the reexamination process, including filing of appeals to the Board of Patent Appeals and Interferences (BPAI) and to the Court of Appeals for the Federal Circuit (CAFC).

It was envisioned that this procedure would decrease the amount of patent litigation. However this has not happened. In part, this is because the third party requestor must accept “statutory estoppel” against subsequent review of issues that could have been raised in the reexamination proceeding. In other words, issues that a patent is invalid because of prior art can not be re-litigated in federal court as part of a defense to an infringement action. The third party requester of the reexamination proceeding must live with the decision of the examiner deciding the reexamination.

As with exparte reexamination, the issues are limited to whether there exists prior art which raises a substantial new question of patentability. Conduct of the patentee is not to be considered. For example, issues of prior sales or fraud by the patentee will not be considered.

What is different in inter partes reexamination from exparte reexamination is that the third party request participates fully in the reexamination process. The third party requestor can file written arguments equal to the patent owner.