The mission of the Department of Defense (DOD) is to provide the military forces needed to deter war and to protect the security of our country. The department's headquarters is at the Pentagon.

The DOD consists of the Departments of the Army, Navy, and Air Force, as well as many agencies, offices, and commands, including the Joint Chiefs of Staff, the Pentagon Force Protection Agency, the National Security Agency, and the Defense Intelligence Agency. The DOD occupies the vast majority of the Pentagon building in Arlington, VA.

The Department of Defense is the largest government agency, with more than 1.3 million men and women on active duty, nearly 700,000 civilian personnel, and 1.1 million citizens who serve in the National Guard and Reserve forces. 

Together, the military and civilian arms of DOD protect national interests through war-fighting, providing humanitarian aid, and performing peacekeeping and disaster relief services.