The National Security Agency (NSA) is an intelligence agency of the United States and comes under the Department of Defense.
The primary purpose of NSA is the collection of foreign communications data and its analysis with regards to the security of American communications against other agencies. The Director of National Intelligence heads the agency.
The NSA headquarter is based 16km from Washington at Fort George G. Meade in Maryland. NSA is one of the most secretive intelligence agencies in the world. For many years the United States government didnt acknowledge its existence. It was jokingly referred as No Such Agency.
NSA is widely thought to be the largest intelligence agency of United states and has a budget larger than CIA. It owns more supercomputers than any organization. It also employs more mathematicians than any other organization. Its scale of operations can be determined by the fact that NSA has electricity bills that exceeds 21 million dollars every year, it has its own exit of the Baltimore Washington parkway and has 18000 parking spaces outside the headquarters.
The NSAs charter prohibits "acquiring information concerning the domestic activities of United States persons" while authorizing it to collect information about foreign intelligence or counterintelligence. Officially the NSA claims to depend on the FBI for information on foreign intelligence activities inside America.
NSA eavesdrops on all forms of intercepted communication including internet and radio broadcast by different individuals and organizations. All confidential, sensitive government communications including diplomatic and military comes under the NSAs secure communications mission. The NSA is heavily involved in cryptanalytic research, and in many technological areas due to its secure communications work for the government. Also, it is involved in the designing of dedicated semiconductors, communications software and hardware.