The National Security Agency is the intelligence bureau of the United States Department of Defense. The agency is headed by the Director of National Intelligence.
NSA was established under the National Security Council Intelligence Directive of 1952. Whereas the CIA deals in HUMINT (gather intelligence using spies), the NSA deals in SIGINT (gathering intelligence using electronic equipment).
Headquartered in Fort Meade, Maryland, the NSA's intelligence assets are estimated to exceed that of the CIA several times over. The agency's responsibilities include collecting foreign intelligence and conducting cryptanalysis. It has developed the world's largest electronic surveillance network, the ECHELON, and it is said that the NSA deals in intelligence that cannot be accessed even with Presidential authority.