18 Corps, 18th Corps, Eighteenth Corps, or XVIII Corps may refer to:
- 18th Army Corps (France)
- XVIII Army Corps (Wehrmacht), a unit of the German Army
- XVIII Corps (German Empire)
- XVIII Reserve Corps (German Empire)
- XVIII Corps (Ottoman Empire)
- 18th Army Corps (Ukraine)
- XVIII Corps (United Kingdom)
- XVIII Airborne Corps, United States
- XVIII Corps (Union Army), a unit in the American Civil War
See also
- List of military corps by number
- 18th Division (disambiguation)
- 18th Brigade (disambiguation)
- 18th Regiment (disambiguation)
- 18th Battalion (disambiguation)
- 18 Squadron (disambiguation)