In military terms, 51st Division or 51st Infantry Division may refer to:
; Infantry divisions
- 51st Division (1st Formation)(People's Republic of China), 1949–1952
- 51st Reserve Division (German Empire)
- 51st Infantry Division Siena (Kingdom of Italy)
- 51st Division (Imperial Japanese Army)
- 51st Division (Philippines)
- 51st Guards Rifle Division
- 51st Rifle Division (Soviet Union)
- 51st (Highland) Division (United Kingdom)
- 51st Infantry Division (United States)