The collection of medieval manuscripts from Alcobaça is one of the most important in the Cistercian world, its scriptorium having remained active from the end of the 12th to the 16th century. More than 460 manuscripts have survived, most of them produced at the abbey, including the 14th-c. Breviary, ms Alc. 66. The written components - namely the calendar, sanctoral, rituals and the additions - contain inconsistencies, and are the object of a detailed analysis in view of dating it accurately. The manuscript is also of interest beyond its liturgical contents, for the illuminations reveal exciting features which differ considerably from other Alcobaça manuscripts. Ms Ale. 66 demonstrates how the identity of the Alcoba9a scriptorium was linked to the local context, while maintaining close ties to other Cistercian abbeys, particularly Ciairvaux.