This book is the first major study of American scientists' encounters with Cold War anticommunism in the decade after World War II. By examining cases of individual scientists subjected to loyalty and security investigations, the organizational response of the scientific community to political attacks, and the relationships between Cold War ideology and postwar science policy, Jessica Wang demonstrates the stifling effects of anticommunist ideology on the politics of science. She exposes the deep divisions over the Cold War within the scientific community and provides a complex story of hard choices, a community in crisis, and roads not taken.