Chapter Six highlights the complex and contested nature of atomic internationalism in the United States between 1945 and 1950. It conceptualizes the introduction of atomic energy into the public sphere as the opening of a new discursive space which was fought over by contending activists and their associated organizations (prominently the Atomic Scientists’ Movement, the World Federalists, the Carnegie Endowment for International Peace, and the United Nations Association). Each struggled to have its vision of international atomic energy governance and world order accepted by the public and the state as official policy. In this chapter, the well-known Baruch and Acheson-Lilienthal Plans emerge as just two of a number of contending schemes for international control. These proposals, the chapter demonstrates, were as much shaped by their authors’ visions of international relations, notions of expertise, and in response to each other, as they were by the desire to tackle an existential threat.