Klaus Emil Julius Fuchs (1911-1988) was a German-born atomic scientist who emigrated to Great Britain in the late 1930s. He worked on the joint U.S./British effort to build the atomic bomb. Following an FBI and British investigation, Fuchs was convicted of espionage in Great Britain for supplying atomic secrets to the Soviet Union. The Fuchs file is tied closely to that of Julius and Ethel Rosenberg, two U.S. citizens who were convicted in 1950 of passing atomic secrets to the USSR. The file ranges from 1949 to 1976.