The Patent Cooperation Treaty (PCT) is a special agreement under Article 19 of the Paris Convention and is open only to states that are members of the Convention. Its main purpose is to make the patent application process simpler and cheaper by having a single set of formal requirements, and a single search and publication procedure, and by postponing translation requirements until thirty months from the priority date. This chapter first discusses the procedure for filing an international application, that is, a PCT application. It then explains the International Preliminary Report on Patentability (IPRP)—a preliminary, non-binding opinion by the international preliminary examining authority (IPEA) on the novelty, inventive step, and industrial applicability of the claimed invention.