Between 1920 and 1950, British and US internationalists called for aviation and atomic energy to be taken out of the hands of nation-states, and instead used by international organizations such as the League of Nations and the United Nations. An international air force was to enforce collective security and internationalized civil aviation was to bind the world together through trade and communication. The bomber and the atomic bomb, now associated with death and devastation, were to be instruments of world peace. Drawing on rich archival research and focusing on public and private discourse relating to the control of aviation and atomic energy, Waqar H. Zaidi highlights neglected technological and militaristic strands in twentieth-century liberal internationalism, and transforms our understanding of the place of science and technology in twentieth-century international relations.