The general rule is that only parties to an action or proceeding—and only parties who are “aggrieved”—may appeal, either as of right or by permission, from an appealable judgment or order. CPLR 5511 codifies this rule by providing that “an aggrieved party or a person substituted for him may appeal from any appealable judgment or order except one entered upon the default of the aggrieved party. He shall be designated as the appellant and the adverse party as the respondent.”

The “party aggrieved” requirement is jurisdictional and subject to inquiry by the court on its own motion even if the respondent has not raised the issue. In Matter of Niagara Mohawk Power v. Green Island Power Authority, 94 N.Y.2d 891 (2000), for example, the appeals were dismissed “by the Court of Appeals, sua sponte, upon the ground that appellants are not parties aggrieved.”