Bad Gandersheim (Eastphalian: Ganderssen) is a town in southern Lower Saxony, Germany, located in the district of Northeim.

During the 10th century, Gandersheim was one of the most important towns of Saxony; the first German poet Hrosvit (Roswitha) lived and worked here until 973.

When a mineral spring was discovered in 1240, Pope Gregory IX initiated the erection of the Holy Spirit hospital.

During World War 2, from October 1944 to April 1945, the town was the site of a subcamp of the Buchenwald Concentration Camp that produced aircraft parts.

This was the unofficial prelude to the summer festival Gandersheimer Domfestspiele, which has been presented yearly on the plaza in front of the abbey church since 1959.