Herzogenburg Monastery (German: Stift Herzogenburg) is an Augustinian monastery located in Herzogenburg in Lower Austria. Founded in 1112 by Augustinian Canons, the monastery was refurbished in the Baroque style in 1714 by Jakob Prandtauer, Johann Bernhard Fischer von Erlach, and Josef Munggenast.
The monastery was founded in 1112 by Ulrich I, Bishop of Passau, at St. Georgen an der Traisen, now in Traismauer, at the confluence of the Traisen with the Danube. In 1244 because of frequent flooding it was moved up-river towards Herzogenburg. From 1714 the buildings were refurbished in the Baroque style by Jakob Prandtauer, Johann Bernhard Fischer von Erlach and Josef Munggenast. The monastery was able to survive the dissolutions enforced by Emperor Joseph II in the late 18th century. Until 1783 the monastery was in the Diocese of Passau, afterwards in the Diocese of St. Pölten.
The monastery church was established in about 1014 by Emperor Henry II and is dedicated to Saint Stephen the Protomartyr (after the patron of Passau Cathedral). In 1112 bishop Ulrich I gave the benefice of Herzogenburg to his newly founded monastery at St. Georgen, which moved to Herzogenburg in 1244.