Lehnin Abbey is a former Cistercian monastery in Lehnin in Brandenburg, Germany. Founded in 1180 and secularized during the Protestant Reformation in 1542, it has accommodated the Luise-Henrietten-Stift, a Protestant deaconesses' house since 1911. The foundation of the monastery in the newly established Margraviate of Brandenburg was an important step in the high medieval German Ostsiedlung; today the extended Romanesque and Gothic brickstone buildings, largely restored in the 1870s, are a significant part of Brandenburg's cultural heritage.