This volume is a lucid and accurate history of the technical research that led to the first atomic bombs. The authors explore how the "critical assembly" of scientists, engineers, and military personnel at Los Alamos, responding to wartime deadlines, collaborated to create a new approach to large-scale research. The book opens with an introduction laying out major themes. After a synopsis of the prehistory of the bomb project, from the discovery of nuclear fission to the start of the Manhattan Engineer District, and an overview of the early materials program, the book examines the establishment of the Los Alamos Laboratory, the implosion and gun assembly programs, nuclear physics research, chemistry and metallurgy, explosives, uranium and plutonium development, confirmation of spontaneous fission in pile-produced plutonium, the thermonuclear bomb, critical assemblies, the Trinity test, and delivery of the combat weapons.