Hirsau Abbey, formerly known as Hirschau Abbey, was once one of the most important Benedictine abbeys of Germany. It is located in the Hirsau borough of Calw on the northern slopes of the Black Forest mountain range, in the present-day state of Baden-Württemberg. In the 11th and 12th century, the monastery was a centre of the Cluniac Reforms, implemented as "Hirsau Reforms" in the German lands by William of Hirsau. The complex was devastated during the War of the Palatine Succession in 1692 and not rebuilt. The ruins served as a quarry for a period of time.

William of Hirsau was a Benedictine abbot and monastic reformer. He was abbot of Hirsau Abbey, for whom he created the Constitutiones Hirsaugienses, based on the uses of Cluny, and was the father of the Hirsau Reforms, which influenced many Benedictine monasteries in Germany. He supported the papacy in the Investiture Controversy. In the Roman Catholic Church, he is a Blessed, the second of three steps toward recognition as a saint.