In this article Professor Van Alstine explores the interaction between the limitations on the doctrine of federal common law and the power of federal courts to interpret the law within the scope of treaties. The article first reviews the constitutional foundation for the operation of treaties as directly applicable ("self-executing") federal law. It then explains that, notwithstanding the Erie doctrine, federal courts may obtain lawmaking powers from either a delegation by Congress or in certain areas of "uniquely federal interest." Professor Van Alstine then argues that the judicial relationship with self-executing treaty law in principle proceeds from the same source of authority as that for Article I legislation. No less than in the statutory context, therefore, a deliberate and circumscribed delegation of lawmaking powers by treaty does not run afoul of federalism or separation of powers limitations on federal common law. Even beyond such an express authorization, the special constitutional nature of treaties also profoundly affects the analysis of the lawmaking powers of federal courts in this context. As a formal expression both of national foreign affairs policy and of the international law obligations of the United States, treaty law operates at the intersection of the two most prominent fields of "uniquely federal interest." As a result, Professor Van Alstine concludes that the decisive interests of national uniformity which arise in the context of formal treaty obligations - and which animate the two noted fields of established federal common law - mandate a different, and ultimately more accommodating, calculus for the interstitial lawmaking powers of federal courts within the scope of self-executing treaties.