Located in Arlington County, Virginia, the Pentagon has been the headquarters for the United States military since 1943. Construction of the unique five-sided building began on September 11, 1941. It houses the largest office space in the world.

Includes index.

What is the Pentagon? -- Snapshot of the Pentagon -- A snapshot in time -- The Pentagon's location -- The Pentagon today -- Outside the Pentagon -- Inside the Pentagon -- Big ideas -- Science behind the Pentagon -- The Pentagon's builders -- Similar structures around the world -- Issues facing the Pentagon -- Activity -- Quiz -- Glossary.