12th Corps, Twelfth Corps, or XII Corps may refer to:
- 12th Army Corps (France)
- XII Corps (Grande Armée), a corps of the Imperial French Army during the Napoleonic Wars
- XII (1st Royal Saxon) Corps, a unit of the Imperial German Army
- XII (Royal Saxon) Reserve Corps, a unit of the Imperial German Army
- XII Corps (India)
- XII Corps (North Korea)
- XII Corps (Ottoman Empire)
- XII Corps (Pakistan)
- 12th Rifle Corps (Soviet Union)
- XII Corps (United Kingdom)
- XII Corps (United States)
- XII Army Corps (Wehrmacht), a German unit World War II
- XII Corps (Union Army), a unit in the American Civil War