An army group is a military organization consisting of several field armies, which is self-sufficient for indefinite periods. It is usually responsible for a particular geographic area. An army group is the largest field organization handled by a single commander – usually a full general or field marshal – and it generally includes between 400,000 and 1,000,000 soldiers.

In the Polish Armed Forces and former Soviet Red Army an army group was known as a Front. The equivalent of an army group in the Imperial Japanese Army was a "general army" (Sō-gun (総軍)).

Army groups may be multi-national formations. For example, during World War II, the Southern Group of Armies (also known as the U.S. 6th Army Group) comprised the U.S. Seventh Army and the French First Army; the 21st Army Group comprised the British Second Army, the Canadian First Army and the US Ninth Army.

In both Commonwealth and U.S. usage, the number of an army group is expressed in Arabic numerals (e.g., "12th Army Group"), while the number of a field army is spelled out (e.g., "Third Army").

The French Army formed a number of groupes d'armées during the First World War.

The German Army formed its first two Heeresgruppen in 1915, to control forces on the eastern front. A total of eight army groups would ultimately be raised – four for service on each front, with one of the eastern front army groups being a multinational German and Austro-Hungarian formation. Originally the Imperial German army groups were not separate formations, but instead additional responsibilities granted to certain army commanders. Crown Prince Wilhelm for instance, was simultaneously commander of the 5th Army and Army Group German Crown Prince from August 1915 to November 1916.

All eight German army groups were named after their commanders.

The Ottoman Army had three army groups: