Occasionally, two or more applications are filed by different inventors claiming substantially the same patentable invention. The patent can only be granted to one of them, and a proceeding known as an “interference” is instituted by the Office to determine who is the first inventor and entitled to the patent. About 1% of the applications filed become involved in an interference proceeding.

Each party to such a proceeding must submit evidence of facts proving when the invention was made. In view of the necessity of proving the various facts and circumstances concerning the making of the invention during an interference, inventors must be able to produce evidence to do this. If no evidence is submitted, a party is restricted to the date of filing the application as his/her earliest date.

The priority question is determined by a board of three administrative patent judges on the evidence submitted. From the decision of the Board of Patent Appeals and Interferences, the losing party may appeal to the Court of Appeals for the Federal Circuit or file a civil action against the winning party in the appropriate U.S. district court.

The interference is a product of our first-to-invent system. An interference is similar to a lawsuit; however, there are substantial procedural differences. The key issue is who was the first to reduce to practice the invention.

Interference proceedings may also be instituted between an application and a patent already issued, provided that the patent has not been issued or the application not been published for more than one year prior to the filing of the conflicting application and provided also that the conflicting application is not barred from being patentable for some other reason.