Throughout his career as director of the FBI, J. Edgar Hoover documented his concerns about Communism, subversion, and anti-American activities in the United States. These concerns are reflected in his March 26, 1947, Testimony before the House Un-American Activities Committee as well as in reams of memoranda and letters he issued to the FBI’s deputy director, agents in charge of FBI field offices, and others. An overriding theme is how the nation and the FBI should respond to these threats, whether real or imagined. In his testimony, he outlines his beliefs about the spread of Communist ideology and specifically about the threat that Communism posed to the United States in the early Cold War period.