Lilienfeld Abbey (Stift Lilienfeld) is a Cistercian monastery in Lilienfeld to the south of Sankt Pölten in Lower Austria. It was founded in 1202 by Leopold VI, Duke of Austria and Styria, as a daughter house of Heiligenkreuz Abbey. Successive abbots acted as councillors to the rulers of Austria, and the abbey became wealthy as a result of this valuable connection.
Abbot Matthew Kollweis (1650–1695) turned the monastery into a fortress during the Turkish advance against Vienna in 1683, installing a garrison and giving shelter to a large number of fugitives. In the 17th century the medieval buildings were extended by Baroque additions. In the first half of the 18th century the tower, library and church interior and furnishings were also refurbished in the Baroque style.