At the end of World War II, J. Robert Oppenheimer was one of America's preeminent physicists. For his work as director of the Manhattan Project, which developed the atomic bomb, he was awarded the Medal for Merit, the highest honor the U.S. government can bestow on a civilian. Yet, in 1953, Oppenheimer was denied security clearance amidst allegations that he was "more probably than not" an "agent of the Soviet Union." Determined to clear his name, he insisted on a hearing before the Atomic Energy Commissions Personnel Security Board. In the Matter of J. Robert Oppenheimer contains an edited and annotated transcript of the 1954 hearing, as well as the various reports resulting from it. Drawing on recently declassified FBI files, Richard Polenberg's introductory and concluding essays situate the hearing in the Cold War period, and his thoughtful analysis helps explain why the hearing was held, why it turned out as it did, and what that result meant, both for Oppenheimer and for the United States.