This Article explores the undertheorized and understudied phenomenon of doubly uncooperative federalism. While most commentary examining the behavior of U.S. states with respect to treaty regimes focuses on cooperative behavior—that is, states that aid in the implementation of duly ratified treaties, or even aid in the implementation of treaties that the federal government has yet to ratify—this Article focuses on settings of doubly uncooperative federalism. There, state action (or inaction) is inconsistent with a duly ratified treaty, and may put the national government in breach of the treaty. The Article elucidates the theoretical underpinnings of doubly uncooperative federalism; discusses doubly uncooperative federalism in practice; explains how constitutional and practical limitations on the federal government’s ability to compel state compliance create a space for doubly uncooperative federalism; exposes shortcomings in ways the federal government might try to minimize doubly un-cooperative federalism; and discusses the consequences of doubly uncooperative federalism—both positive and negative.