This is a substantial reinterpretation of the wartime Anglo-American relationship on atomic energy. Using the recently declassified American and British archives, this essay maintains that the relationship was defined primarily by Roosevelt and Churchill, and that they realized that it represented, potentially, the cornerstone of a postwar Anglo-American entente in which only these "two policemen" (the United States and Britain) would have the atomic bomb. This essay suggests a new interpretation of Roosevelt as a shrewd administrator in this important area and also offers a new interpretation of his wartime foreign policy: his understanding of power, his attitudes toward the Soviet Union, his view of the United Nations, and his expectations about the postwar world. He was not naïve or innocent, but astute, about power in international affairs. He did not trust the Soviet Union and kept in reserve the military power to change her policy. He was not a Wilsonian internationalist but a firm believer in big-power politics.