Post-grant opposition permits third parties to challenge the validity of a patent after it has been granted.
The opposition must be filed within a specific period after the patent grant, commonly ranging from six to twelve months, depending on the jurisdiction.
Among the countries that have an opposition system, procedural and substantive requirements have some common aspects, but are different in details.
[16][17] The term for filing an opposition with the National Institute of Industrial Property (INPI) is nine months from the grant of the French patent.
[17][18] Under United States patent law, an opposition proceeding is called a reexamination.
Subsequent to the Leahy–Smith America Invents Act (2011), any third party can challenge the validity of an issued patent using either post-grant review under 35 U.S.C.