21st Division or 21st Infantry Division may refer to:
Infantry divisions 21st Division (People's Republic of China) 21st Infantry Division (France) 21st Division (German Empire) 21st Landwehr Division, German Empire 21st Reserve Division, German Empire 21st Infantry Division (Wehrmacht), Germany 21st Parachute Division, Germany 21st Waffen Mountain Division of the SS Skanderbeg, Germany 21st Mountain Division (India) 21st Division (Iran) 21st Infantry Division "Granatieri di Sardegna", Kingdom of Italy 21st Division (Imperial Japanese Army) 21st Division (Philippines) 21st Mountain Infantry Division (Poland) 21st Infantry Division (Russian Empire) 21st Infantry Division (South Korea) 21st Division (South Vietnam) 21st Guards Motor Rifle Division (Russia) 21st Guards Airborne Division, Soviet Union 21st Guards Mechanized Division, later the 21st Guards Motor Rifle Division, Soviet Union 21st Guards Rifle Division, Soviet Union 21st Motor Rifle Division, Soviet Union 21st Motor Rifle Division NKVD, Soviet Union 21st Rifle Division (Soviet Union) 21st Division (Spain) 21st Division (United Kingdom) 21st Airborne Division, United States deception formation during WWII 21st Division (Yugoslav Partisans)
Cavalry divisions 21st Cavalry Division, United States
Armoured divisions 21st Armoured Division (Egypt), part of the Western Military Region (Egypt) 21st Panzer Division, Wehrmacht, Germany 21st Guards Tank Division, Soviet Union 21st Armored Division (United States), a division of the U.S. Army
Aviation divisions 21st Air Division, United States 21st Aviation Division, Yugoslavia
See also 21st Army (disambiguation) XXI Corps (disambiguation) 21st Brigade (disambiguation) 21st Regiment (disambiguation) 21st Battalion (disambiguation) 21st Squadron (disambiguation)