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)