The Pentagon is the headquarters of the United States Department of Defense, located in Arlington County, Virginia. As a symbol of the U.S. military, "the Pentagon" is often used metonymically to refer to the U.S. Department of Defense rather than the building itself.

The Pentagon is the world's largest office building by floor area, with about 6,500,000 sq ft , of which 3,700,000 sq ft are used as offices. Approximately 28,000 military and civilian employees and about 3,000 non-defense support personnel work in the Pentagon.

It has five sides, five floors above ground, two basement levels, and five ring corridors per floor with a total of 17.5 mi of corridors. The Pentagon includes a five-acre central plaza.