Interference proceeding

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In United States patent law, an interference proceeding, also known as a priority contest, is an inter partes proceeding to determine the priority issues of multiple patent applications. Unlike in most other countries, which have long had a first-to-file system, until the enactment of the Leahy–Smith America Invents Act (AIA) in 2011, the United States operated under a first-to-invent. The interference proceeding determines which of several patent applications had been made by the first inventor.

The AIA switched the US to a first-to-file regime effective March 16, 2013,^[1] and interferences apply only to patent applications with an effective filing date prior to that change.