Although a body of law has developed around the use of confidential informants in criminal investigations, the role of informants in national security matters is less clearly defined. This Note first examines the limitations on the use of informants in the criminal context that are imposed by the Fourth Amendment, a detailed set of guidelines issued by the Attorney General, and other sources of law. It then turns to the treatment of informants by the major sources of national security law, including the Foreign Intelligence Surveillance Act. Ultimately, this Note concludes that in the national security context, government agents are free from many of the restrictions placed on the use of informants in criminal investigations. Although this relative freedom may be necessary given the immediate challenge of combating international terrorism, care should be taken that the executive branch does not use informants in a way that violates individual privacy or oversteps other proper investigative boundaries.