XXI Corps

21 Corps, 21st Corps, Twenty First Corps, or XXI Corps may refer to:


 * XXI Corps (German Empire), a unit of the Imperial German Army prior to and during World War I
 * XXI Corps (Ottoman Empire), active during World War I
 * XXI Corps (United Kingdom), active during World War I
 * Indian XXI Corps, active during World War II
 * XXI Corps (India), currently active Indian Army corps
 * XXI Corps (United States), active during World War II
 * XXI Corps (Union Army), active during the American Civil War
 * XXI Mountain Corps (Wehrmacht), active during World War II