The Patent Cooperation Treaty is often referred to as the PCT. It is an international treaty that governs patent filings and cooperation amongst member states. The Patent Cooperation Treaty came into being as far back as 1970 with the aim of unifying patent filing procedures and to ensure that the patents granted in the member states are protected against infringement thereof. Although there certainly is no such thing as an international patent, the term used for the filing of patents under the Patent Cooperation Treaty is known as the international filing or application. It can also be referred to as a PCT filing.

Under the Paris Cooperation Treaty only one application needs to be lodged with the Receiving Office. It can be done in one language. The International Searching Authority, which is more often referred to as ISA, then does a search. Once the search has been completed, ISA provides an opinion in writing about the application. The invention must be deemed patentable for application to go onto the next phase. In some instances the IPEA, which stands for International Preliminary Examination Authority will also perform an examination. The last phase of a patent application with the Patent Cooperation Treaty involves another examination by the national patent authority.

The World Intellectual Property Organisation, known as WIPO, administers the PCT. In effect the member states of the Paris Convention, who are signatories to the Paris Cooperation Treaty, number more than 124 and as such it is possible to file a single patent application to cover all the countries, although each country must still authorise the patent after their national or regional examination. To file an international application you must be resident in one of the Paris Patent Cooperation Treaty signatory countries.