Interference proceeding (patent)


An interference proceeding, also known as priority contest, is an inter partes proceeding to determine the priority issues of multiple patent applications. It is a unique patent law concept of the United States. Unlike most other country that adopts the first to file system, the first to invent system of the U.S. allows a party who failed to file a patent application on time to challenge the inventorship against another party with a granted or pending patent if certain requirements are met.


The interference proceeding is an administrative proceeding conducted by an administrative law judge (administrative patent judge) of the United States Patent and Trademark Office (USPTO) to determine which applicant is entitled to the patent if the same invention is claimed:

  1. in two pending applications, or
  2. in one pending application and a patent issued within a year of the pending application's filing date.

The Board of Patent Appeals and Interferences, a quasi-judicial body in the USPTO, hears interference contests. Its final judgment designating one party in an interference contest as the first inventor is called priority award or simply award. The U.S. Court of Appeals for the Federal Circuit hears appeals from this tribunal.


At least two parties are involved in an interference proceeding. The inventor who filed patent application earlier is called "senior party", the rest of the inventors are "junior parties". Both parties can be referred as "contestants", but currently, it is more likely used to describe the junior party.

  • Senior party: Merely being the first to file the application does not grant a party legal protection. It only counted as prima facie evidence that he/she is the first inventor. It can also file a "motion to dissolve interference" to request the dismissal of challenges to its priority.
  • Junior party: Party or parties other than the senior party. A junior party bears the burden of proving that he or she is the first inventor. The proceeding's administrator takes certain factors, say the invention's conception date and the inventor's diligence in reducing the invention to practice, into account. Before 1960s, a junior party were frequently called "interferant".

Burden of proof

The burden of proof issues are defined in 37 C.F.R. 1.657:

(a) A rebuttable presumption shall exist that, as to each count, the inventors made their invention in the chronological order of their effective filing dates. The burden of proof shall be upon a party who contends otherwise. (b)In an interference involving copending applications or involving a patent and an application having an effective filing date on or before the date the patent issued, a junior party shall have the burden of establishing priority by a preponderance of the evidence. (c)In an interference involving an application and a patent and where the effective filing date of the application is after the date the patent issued, a junior party shall have the burden of establishing priority by clear and convincing evidence.

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