In law, ex parte () is a Latin term meaning literally "from/out of the party/faction of" (name of party/faction, often omitted), thus signifying "on behalf of (name)". An ex parte decision is one decided by a judge without requiring all of the parties to the dispute to be present. In English law and its derivatives, namely Australian, New Zealand, Canadian, South African, Indian, and U.S. legal doctrines, ex parte means a legal proceeding brought by one party in the absence of and without representation of or notification to the other party.

The term is also used more loosely to refer to improper unilateral contacts with a court, arbitrator, or represented party without notice to the other party or counsel for that party. The phrase was common in the titles of habeas corpus and judicial review cases until the end of the twentieth century, because those cases were originally brought by the Crown on behalf of the claimant. In Commonwealth common law jurisdictions, the title typically appeared as R v (Defendant), ex parte (Claimant); in the US, this was shortened to Ex parte (Claimant). A proceeding in an executive agency to establish a right, such as patent prosecution, can also be ex parte.