The 51st Infantry Division Siena () was a regular infantry division of the Italian Army during World War II. The Siena Division was fully mobilized in August 1940, for service in the occupation of Albania in the following September. It took part in the Greco-Italian War as part of the Italian VIII Corps suffering heavy losses. It was next used as an occupation force and in May 1941, was located in the Peloponnese before being transferred to the island of Crete and joining the Italian XXVI Corps in September 1941. It remained in Crete until September 1943, when Italy surrendered to the Allies and the division was disarmed by the Germans.