An interference proceeding, also known as a priority contest, is an inter partes proceeding to determine the priority issues of multiple patent applications. It is a proceeding unique to the patent law of the United States. 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, and interferences apply only to patent applications with an effective filing date prior to that change. Definition An interference proceeding is an administrative proceeding conducted by a panel of administrative patent judges (administrative law judges sitting on the Board of Patent Appeals and Interferences) of the United States Patent and Trademark Office (USPTO) to determine which applicant is not entitled to the patent if both claimed the same invention in: two or more pending patent applications, or at least one pending patent application and at least one patent issued within a year of the pending application's filing date. A panel, composed of judges on the Board of Patent Appeals and Interferences, a quasi-judicial body in the USPTO, hears an interference contest. Its final judgment adjudicating one party as an earlier inventor is called a priority award, or simply an award. Appeals from this tribunal are heard before either the United States Court of Appeals for the Federal Circuit or the United States District Court for the District of Columbia. See , . Parties At least two parties are involved in an interference proceeding: the inventor(s) or applicant(s) who filed an earlier patent application are called the "senior party", and the other inventor(s) or applicant(s) are called the "junior party". Both parties can be referred as "contestants", but that term is currently more likely to be used to describe the junior party. Senior party: Merely being the first to file the application does not grant a party legal protection. It counts only as prima facie evidence that he or she is the first inventor. A senior party can also file a "motion to dissolve interference" to request the dismissal of challenges to its priority. Junior party: A party other than the senior party bears the burden of proving that he is the first inventor. The