Ancillary Jurisdiction Law and Legal Definition

Ancillary jurisdiction allows a particular claim or party to be joined to an action without an independent jurisdictional basis. Ancillary jurisdiction may be exercised in the case of compulsory counterclaims, impleader of third parties, interpleader, and intervention as of right. Federal courts may exercise ancillary jurisdiction over a case or dispute, regardless of the citizenship of the parties or the amount in controversy, mostly in the interest of judicial economy and convenience to the parties.

The Federal Rules of Civil Procedure expressly authorize the exercise of ancillary jurisdiction in the instance of a compulsory counterclaim. The rules state that the defendant is required to bring and compulsory counterclaims, which must be recognized by the federal court regardless of an independent basis for jurisdiction.