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Prosecution laches doctrine is an equitable doctrine applied in patents law. Under this doctrine, the holder of a valid patent nonetheless may be barred from enforcing it if there was an unreasonable and unexplained delay in prosecuting the patent claim, and the alleged infringer has suffered prejudice as a result. The primary purpose behind the prosecution laches doctrine is to protect the public's intervening adverse rights. A patentee may tread on the public's intervening adverse rights by engaging in one of two tactics, or a combination of the two. The patentee may engage in "submarine patenting," i.e., s/he may file a patent application and then unduly delay prosecution such that a patent does not issue for many years. The application acts like a submarine, undetected and waiting to be used. Once the public, unaware of the pending application, expends time, effort, and resources to further advance the same technology, the patent suddenly issues, or surfaces, and the patentee attempts to reap the pecuniary rewards. In the alternative the patentee can timely prosecute an application before the United States Patent and Trademark Office, obtain a patent, wait for intervening developments in the field, and then seek issuance of additional, presumably broader patents covering that technology. [MOSAID Techs. Inc. v. Samsung Elecs. Co., 362 F. Supp. 2d 526 (D.N.J. 2005)]
A textbook case of prosecution laches, if one exists, involves a patent application filed and then followed by a lengthy period of unexplained inactivity. Prosecution laches is not a doctrine, like traditional laches, aimed to protect specific competitors. It rather serves the broader public interests in the timely issuance of patents. Because prosecution laches applies to the conduct of a patent applicant prior to the issuance of a patent, the doctrine cannot be aimed at protecting specific infringers or potential infringers from prosecutorial delay, because there can be no infringement until a patent has issued. [Reiffin v. Microsoft Corp., 270 F. Supp. 2d 1132 (N.D. Cal. 2003)].