Battalion, a military unit usually numbering between 500 and 1,000 men. This term has been loosely used in many countries for centuries to mean any large body of troops. Historically, the next higher unit above a battalion is a regiment. In the U.S. Army, however, regiments no longer exist as tactical units, and the next higher unit is a brigade. A battalion consists of two or more companies. Normally a battalion is commanded by a lieutenant colonel.

During World War II and the Korean War an infantry battalion of the U.S. Army consisted of three rifle companies, a heavy weapons company (machine guns and mortars), and a headquarters company. Artillery batteries and companies of noncombat troops were also formed into battalions. When the brigade replaced the regiment, the structure of infantry battalions became more flexible.