Until passage of the Leahy-Smith America Invents Act (AIA), interference proceedings were a unique and important feature of the U.S. patent system. Interferences were declared when two different parties filed a patent application claiming the same invention.
In addition to relying upon the filing date of their patent applications, the parties could submit research records and testimony of inventors and corroborators in an effort to show that they were first to invent. No other patent system in the world used interferences. Instead, most countries have a first-to-file system, where a dispute between parties filing patent applications claiming the same invention is generally resolved by looking at who has the earliest filing date.