Corporal is a military rank in use in some form by many militaries and by some police forces or other uniformed organizations. Within NATO, each member nation's corresponding military rank of corporal is combined under the NATO-standard rank scale code OR-3 or OR-4. However, there are often differences in how each nation (or service in each nation) employs corporals. Some militaries don't have corporals, but may instead have a Junior Sergeant.

In some militaries, the rank of corporal nominally corresponds to commanding a section or squad of soldiers. However, in the United States Army, the rank of corporal is considered a "lateral promotion" from E-4 Specialist and usually only occurs when the soldier has been selected by a promotion board to become an E-5 Sergeant and is serving in an E-5 billet such as a fireteam leader in a rifle squad. The lateral promotion is used to make the soldier a non-commissioned officer without changing the soldier's pay. As the Table of Organization & Equipment (TO&E) rank of a fire team leader is sergeant and that of squad leader is staff sergeant. In the United States Marine Corps, corporal is the Table of Organization (TO) rank for a rifle fire team leader, machine gun team leader, light mortar squad leader, and assault weapon squad leader, as well as gunner on most larger crew served weapons (i.e. medium mortars, heavy machine guns, and anti-tank missiles), armored vehicles (e.g. tanks, light armored vehicles, and armored assault vehicles), and the two assistant gunners on a howitzer (the gunner is a sergeant).

In most countries that derive their military structure from the British military system, corporal is a more senior rank than that of private. However, in several other countries, such as Canada, Italy and Norway, corporal is a junior rank, indicating a more experienced soldier than a private, and also on a higher pay scale, but having no particular command appointment corresponding to the rank, similar to specialist in the U.S. Army.