A type of administrative action that takes place in the United States Patent and Trademark Office and arises because the U.S. has a first-to-invent patent system. An interference arises when two parties claim the same invention and is in essence litigation to determine who invented it first. US interference practice should effectively end as a result of the America Invents Act although interferences can be expected to continue for patents filed before the AIA’s effective date for all applications to become First-to-File (i.e., March 16, 2013), but dwindle away over time.