inter partes

Inter partes is Latin for “between parties.” In litigation, it refers to any proceeding in which all interested parties are given notice and an opportunity to be heard, as opposed to ex parte proceedings, which involve only one party. The term also applies in contract law, where it denotes rights and obligations that exist only between the parties to a contract. 

In U.S. patent law, inter partes review (IPR) is an administrative procedure conducted by the Patent Trial and Appeal Board (PTAB) within the United States Patent and Trademark Office (USPTO). It allows third parties to challenge the validity of an issued patent based on prior art, typically under 35 U.S.C. §§ 102(a) and 103(a). This procedure provides an alternative to federal court litigation under certain conditions.

Notably, an administrative determination by the USPTO that a patent is invalid can override an earlier federal court judgment that determined the same patent was valid. This principle was affirmed in Fresenius USA, Inc. v. Baxter Int’l, Inc., 721 F.3d 1330 (Fed. Cir. 2013), where a final PTAB decision invalidating a patent nullified a district court’s earlier infringement judgment based on that patent.

See also: See: 35 U.S.C. §§ 311 – 319.

[Last reviewed in July of 2025 by the Wex Definitions Team] 

Wex

• COMMERCE
• commercial activities
• PROPERTY
• THE LEGAL PROCESS
• administrative law
• courts
• judicial administration
• business law
• commercial law
• contracts
• wex definitions
• courts and procedure
• intellectual property
• patent law
• legal education and practice