This Essay explores American unilateralism and the divergence between American and European attitudes toward international law. The United States, Professor Rubenfeld shows, has always displayed unilateralist tendencies. Since 1945, however, while Europe has grown ever more internationalist, the United States has spoken out of both sides of its mouth, acting both as a world leader in forging the new international order and as the world’s chief locus of resistance against that order. To understand this phenomena, Professor Rubenfeld argues, it is crucial to distinguish between two conceptions of constitutional law. “Democratic constitutionalism” sees constitutional law as the foundational law a particular polity has given itself through a special act of popular lawmaking. “International constitutionalism” sees constitutional law not as an act of democratic self-government, but as a check or restraint on democracy, deriving its authority from its expression of universal rights and principles that transcend national boundaries. The international charters and institutions that emerged after the Second World War were built on the premises of international constitutionalism. This development was broadly acceptable among elites in Europe, where World War II had come to exemplify the potential horrors of both nationalism and democracy. As a result, the true challenge international law’s supporters face today is that the existing international governance institutions are not only antinationalist, but antidemocratic–and not by accident, but by structure and design. To this extent, America, with its longstanding commitment to democratic constitutionalism, does in fact have good reason to resist international governance today. Drawing on this conclusion, Professor Rubenfeld suggests principles that could guide U.S. relations to international governance regimes, showing the kinds of international law that America could embrace without compromising its commitment to self-government.