The American jurist James Brown Scott, at one time, the main legal officer of the State Department, a founder of the American Society of International Law, and of the Carnegie Endowment for International Peace, was a central figure in the development and professionalization of international law in the United States in the early twentieth century. He was also very influential in the direction the historiography of the subject has subsequently taken, and in particular in its engagement with the so- called School of Salamanca of the sixteenth and seventeenth centuries, of which Francisco de Vitoria was the supposed “founder.” For Scott, Vitoria’s attempt to re- describe the earlier “law of nations” in such a way that while it remained firmly grounded in natural law, it became also a form of positive law was the foundational moment for modern international law. Vitoria had supposedly transformed what had earlier been only law between citizens and non- citizens of the Roman world into a truly global law which was both prior and superior to any form of civil law and thus equally applicable to both the Europeans and non- Europeans. But Scott’s interest in Vitoria was not solely antiquarian. It was also crucial for his contribution to a series of debates over the future of international law, and international relations more widely, in the turbulent years after the end of First World War, a period which saw the rise of the United States as a global power and the creation of the first truly international legal and political institutions, the League of Nations and the Permanent Court of International Justice. For Scott himself, the two most pressing concerns, and the ones for which Vitoria’s conception of the “law of nations” was central, were his bid to demonstrate the enduring significance of the Catholic natural law tradition for modern international law, at a time when positivism had seemingly diminished it forever, and, paradoxically perhaps, to support the increasing demands for an international recognition of equal rights for women.