Gandersheim Abbey is a former house of secular canonesses (Frauenstift) in the present town of Bad Gandersheim in Lower Saxony, Germany. It was founded in 852 by Duke Liudolf of Saxony, progenitor of the Liudolfing or Ottonian dynasty, whose rich endowments ensured its stability and prosperity. His coffin is still in the abbey church, yet contents are unknown. The canonesses, commonly known as Stiftsdamen, were allowed private property and as they had taken no vows, were free at any time to leave the abbey. The Ottonian and Salian kings and their entourages often stayed in Gandersheim, and the canonesses were by no means remote from the world. Apart from the memorial masses for the founding family, one of the main duties of the canonesses was the education of the daughters of the nobility (who were not obliged to become canonesses themselves).
The Reformation was first introduced into the Principality of Brunswick-Wolfenbüttel in 1542 when troops of the Schmalkaldic League occupied it. The Reformers ignored the abbey's Imperial immediacy and ordained the use of Lutheran church services, the introduction of which however the canonesses were able to postpone on account of the absence of the prioress (Dekanin) who was governing the abbey on behalf of the seven-year-old abbess. The townspeople of Gandersheim had received the Reformation enthusiastically and on 13 July 1543 undertook an iconoclastic attack on the abbey church, where they destroyed images and altars. Henry V, changed his mind however and the principality changed back to Roman Catholicism. He made good at least some of the damages, and the church was re-dedicated.
In 1802, faced with imminent secularisation, the abbey surrendered its Imperial immediacy to the sovereignty of the Dukes of Brunswick-Wolfenbüttel, thus ending the centuries-long struggle with the Welfs.
During the French occupation Gandersheim belonged to the Kingdom of Westphalia. The abbess, who had fled, was permitted by Napoleon to return to the abbey and to live there until her death on 10 March 1810, after which there were no further elections for a successor. The abbey was dissolved, its assets were taken by the Westphalian crown and the remaining occupants pensioned off.
Even after the end of the Kingdom of Westphalia in 1813 the Duchy of Brunswick did not restore the abbey.
The abbey is now used by the Evangelical-Lutheran parochial group of St. Anastasius and St. Innocent. During restoration works in 1997 there came to light some of the old church treasure: relics, textiles and reliquaries.