In 1290, members of the de Viane family donated a six-volume set of large, deluxe liturgical manuscripts to the Cistercian nuns of Beaupré in Grimminge, East Flanders. The three extant volumes and a later supplement are now known as the Beaupré Antiphoner (Baltimore, Walters Art Museum, W. 759-762). The nuns used, extensively revised, and supplemented the antiphoner for the next five hundred years until the abbey was suppressed in 1796 during the French Revolution. The manuscript offers a bottom-up perspective on the history of Cistercian chant in a women’s community. It also fills lacunae in the documentary sources related to reform and change in the history of the abbey. Revisions made in the late fifteenth century under the Observant movement suggest a revival of interest in St. Bernard and the “Bernardine” recension of Cistercian chant. Further alterations in the early modern period demonstrate that the nuns did not abandon their medieval chant tradition and adopt post-Tridentine versions until the late eighteenth century, approximately two hundred years after the publication of the Roman breviary of Pope Pius V (1568). The nuns viewed their carefully considered revisions as a necessary condition of continuity, not as a threat to it.