What international treaty enables a single patent application for multiple countries?

The international treaty that enables a single patent application for multiple countries is the Patent Cooperation Treaty (PCT).

Adopted in Washington in 1970 and administered by the World Intellectual Property Organization, the PCT lets an eligible applicant file one international application instead of immediately filing separate applications in every desired country. The application has the effect of a national application in the participating states and includes an international search and preliminary examination process.

A common misconception is that the PCT grants a worldwide patent. It does not. After the international phase, the applicant must enter the national or regional phase in the jurisdictions where protection is wanted, pay local fees, provide translations where required, and satisfy each office’s patentability rules.

The Paris Convention is a related but different route: it helps applicants claim priority from an earlier filing, while the Madrid Protocol concerns international trademark registration and the Berne Convention concerns copyright.