This essay investigates the intellectual history of one of the purportedly most “revolutionary” concepts of post-1945 international thought—the concept of supranationality. While the literature has generally analyzed the concept as a direct continuation of progressive cosmopolitan ideas, or, to the contrary, as a political watchword formulated after 1945 to promote the European project, this essay highlights other, more ambiguous origins for the concept. It retraces the early uses of the concept in French debates. It argues that the irruption of supranationality in the political and legal vocabulary was far from revolutionary, as is typically claimed—without referring directly to the writings of the great classical philosophers. Rather, the concept drew on earlier discourses whose emergence can be identified in late nineteenth- and early twentieth-century debates, ranging from Catholic thought to international law. To retrace the genealogy of supranationality in the decades preceding the supranational vogue of the 1950s contributes to illuminating the complex intellectual origins of the European Union and of international thought more generally.