The 31st Infantry Division was a division of the Philippine Army under the United States Army Forces in the Far East (USAFFE).

The Philippine Army (PA) is the main, oldest and largest branch of the Armed Forces of the Philippines (AFP), responsible for ground warfare and as of 2021 had an estimated strength of 143,100 soldiers backed by 131,000 ready reserves. The service branch was established on December 21, 1935, as the Philippine Commonwealth Army. The Philippine Army has engaged in many conflicts including the ongoing Communist rebellion in the Philippines, the Moro conflict and, alongside other national military forces, in conflicts of international scope.