Security agency

A security agency is a governmental organization which conducts intelligence activities for the internal security of a nation. They are the domestic cousins of foreign intelligence agencies, and typically conduct counterintelligence to thwart other countries' foreign intelligence efforts. For example, the United States Federal Bureau of Investigation (FBI) is the internal intelligence, security and law enforcement agency, while the Central Intelligence Agency (CIA) is an external intelligence service, which deals primarily with intelligence collection overseas. A similar relationship exists in Britain between MI5 and MI6.

The distinction, or overlap, between security agencies, national police, and gendarmerie organizations varies by country. For example, in the United States, one organization, the FBI, is a national police, an internal security agency, and a counterintelligence agency. In other countries, separate agencies exist, although the nature of their work causes them to interact. For example, in France, the Police nationale and the Gendarmerie nationale both handle policing duties, and the Direction centrale du renseignement intérieur handles counterintelligence.