The Department of Defense (DoD, USDOD, or DOD) is an executive branch department of the federal government of the United States charged with coordinating and supervising all agencies and functions of the government concerned directly with national security and the United States Armed Forces. The Department is also the largest employer in the world, with 1.3 million active duty servicemen and women (as of 2015). Adding to the total is over 820 thousand National Guardsmen and Reservists from the four services, and over 740 thousand civilians bringing the total to over 2.8 million employees. It is headquartered at the Pentagon in Arlington, Virginia, just outside of Washington, D.C.