Marshall Rosenbluth was an American physicist who worked in the theoretical division at Los Alamos from 1950 to 1956. In this interview, Rosenbluth addresses the theoretical issues involved in designing both the atomic and hydrogen bombs. He discusses how the pressure to create a nuclear bomb before the Soviet Union affected work in the laboratory, especially in performing and checking calculations. Rosenbluth also recounts his experiences during the nuclear weapons tests at Los Alamos and Bikini Atoll. He recalls the roles of top scientists, like Edward Teller, Hans Bethe, Enrico Fermi, and Carson Mark, in the building of the hydrogen bomb. He also explains how funding and other external factors affected the hydrogen bomb’s design.