This chapter examines the post-World War II development of international humanitarian law, focusing specifically on the Geneva Conventions. Beginning with an overview of the history of the Geneva Conventions, it examines how the experience of World War II and the early Cold War shaped the creation of civilian immunity norms in the immediate postwar period. Specifically, it uses archival records to show how Western states and the Soviet Bloc used emotional moral rhetoric and legal discourse to construct a relatively permissive regime of law. It begins by examining how states used moral intuitions and legal rhetoric to discuss norms concerning strategic bombing and nuclear weapons use during the negotiations over the 1949 Geneva Conventions. Next, it examines the creation of the modern principles of distinction and proportionality during the negotiations over the Additional Protocols to the Geneva Conventions in 1977.