Riddagshausen Abbey (Kloster Riddagshausen) was a Cistercian monastery just outside the city of Brunswick in Germany. It was founded as Marienzelle by Ludolf the Wend, a ministerialis of Henry the Lion and steward of Brunswick, and settled in 1145 by monks from Amelungsborn Abbey. Henry endowed the new foundation in 1146 with the neighbouring village of Riddagshausen, from which it took its name. The abbey early acquired reichsunmittelbar status as an Imperial abbey. The site, now included within the city of Brunswick, is now mostly a nature reserve and arboretum.