The Mont Saint-Michel abbey in Normandy, France, was an important pilgrimage site in Christianity, and its scriptorium produced numerous manuscripts between the end of the 10th and the middle of the 13th century. The present study investigates the practice of the Mont Saint-Michel scriptorium in the use of parchment to produce manuscripts in the 11th century, based on a corpus of 67 manuscripts produced between 980 and 1100. The combination of information gained from the codicological studies, proteomic analyses and thickness measurement of the parchments, revealed that copyists and/or artists deliberately select the type of skin depending on the content of the folio or the status of the manuscript. Thus, only sheep parchment is used for folios with text or only lightly illuminated manuscripts, while calf parchment is selectively used for the most valued part in the manuscript, such as full-page illuminations and often large ornate letters opening the manuscripts. For the most prestigious manuscripts, which concern four volumes in the corpus, calfskin is used in the entire manuscript, with the occasional addition in the Mont Saint Michel Sacramentary of goatskin, confirming the special status of these manuscripts for liturgical use. The demonstration of these practices constitutes for historians invaluable information on the parchment production at the time, as well as insight into the manuscript or folio significance.