The 21st Division was one of the divisions of the Spanish Republican Army that were organized during the Spanish Civil War on the basis of the Mixed Brigades. Situated on the Andalusian front, the division played a minor role.
The unit was created on 3 April 1937, within the Army of the South. The 21st Division was born from the militarization of the old Granada sector. It was made up of 76th, 79th and 80th mixed brigades, with its headquarters in Jaén. As of June 1937, the division was integrated into the IX Army Corps.