This Note defends the majority's standing analysis in Massachusetts v. EPA as a matter of both jurisprudence and public policy. First, this Note recounts the Court's state standing cases, tracing the development of the parens patriae doctrine that permits states to litigate in defense of interests related to their status as sovereigns. Massachusetts sits at the intersection of this jurisprudence and the Court's recent debate over the Purposes of standing. Massachusetts built upon cases that held the assurance Of concrete adversarialism-rather than upholding the separation of powers-as the primary purpose of standing. In Massachusetts, Justice Stevens focused on both a traditional injury to Massachusetts's property and plaintiff's status as a sovereign state to find that the parties were truly adverse. Contrary to Chief justice Roberts's dissent and early criticism, justice Stevens did not use Massachusetts's statehood to obfuscate the traditional standing requirements. The majority advanced cumulative, but doctrinally distinct, routes to standing. Understanding parens patriae as separate from the traditional constitutional standing inquiry necessitates the development of a rationale justifying different standards for state plaintiffs. This Note seeks to do that by providing a unifying principle for state standing drawn from economics. Economists would label as 'public goods" the precise set of interests that the Court has found to support claims of parens patriae standing. This Note concludes by exploring some analytical wrinkles and beneficent consequences of linking state standing to the provision of public goods within the context of our system of dual sovereignty.