In Michigan law, the true interested party rule recognizes that litigation should only be initiated by a party who has an interest that provides sincere and vigorous advocacy. [1] In law, the real interested party is the one who actually holds the substantive right claimed and who has the legal right to enforce the claim (under the applicable substantive law). In addition, the “true interested party” must bring an action on its own behalf. In many situations, the parties themselves (i.e. the plaintiff and the defendant) are the true interested party. n. the person or entity that will benefit from a lawsuit or application, even if the plaintiff (the person filing the claim) is someone else, often referred to as a “nominal” plaintiff. Example: A trustee sues a person who damaged a trust property; The real interested party is the beneficiary of the trust. If the funds held by a party are held by a financial institution on behalf of, but not necessarily in trust (e.g., a bank chequing account is seized by a third party claiming a valid outstanding debt), the bank is generally sued as a nominal defendant. Of course, the real part is in the interest of the account owner, who has an absolute right to intervene and protect his assets. If a trustee is a party to a dispute, the actual portion is in the interest of the beneficiary of the trust. In the United States, Rule 17 of the Federal Rules of Civil Procedure expressly provides that the trustees are the effective party in the interest when it is necessary to bring an action on behalf of the estate. A beneficiary may institute proceedings in these circumstances only if the trustee refuses or refrains from bringing an action.

Under California law, when a case is submitted to a writ of warrant (California version of mandamus), the appellant goes first in signing the case in the appeal as plaintiff, and the superior court becomes the defendant. The real adversary is then listed under these names as a “real party in interest”. Thus, a number of famous California cases such as Burnham v. Superior Court of California (1990) ended with such unusual names.