The Internal Security Act of 1950, 64 Stat. 987, also known as the Subversive Activities Control Act of 1950, the McCarran Act after its principal sponsor Sen. Pat McCarran (D-Nevada), or the Concentration Camp Law, is a United States federal law. Congress enacted it over President Harry Truman's veto. It required Communist organizations to register with the federal government. The 1965 U.S Supreme Court ruling in Albertson v. Subversive Activities Control Board saw much of the act's Communist registration requirement abolished. The emergency detention provision was repealed when the Non-Detention Act of 1971 was signed into law by President Richard Nixon. The act's Subversive Activities Control Board, which enforced the law's provision calling for investigations of persons engaging in "subversive activities," would also be abolished in 1972.

Patrick Anthony McCarran was an American farmer, attorney, judge, and Democratic politician who represented Nevada in the United States Senate from 1933 until 1954.