The fourteenth-century fragments of mensural polyphony housed at theUtrecht University Library (NL-Uu 6 E 37, Hs. 1846) have long been associated with the court of the Counts of Holland at The Hague and one of the pre-eminent collegiate churches of Flanders, St Donatian in Bruges (Strohm 1984; Strohm 1985). A in-depth investigation of the host books from which the fragments of the sub-collection Uu 37.I were extracted in the early twentieth century now reveals previously overlooked ties to ecclesiastical institutions in Utrecht. More specifically, research carried out in Part I of this dissertation points to collegiate chapters some of whose canons were exceptionally wealthy, belonging to the city’s most important patrician families. Codicological and palaeographical analyses, moreover, revealed that the fragment leaves of Uu 37.I belonged to four different convolutes one of which, according to its foliation, used to be an extensive collection of presumably Mass settings and motets. Part 2 of this dissertation is dedicated to late-medieval Utrecht. Being an episcopal city, Utrecht was home to a great number of ecclesiastical institutions, ranging from monasteries to parish churches. Most influential at the time, however, were the two wealthy collegiate chapters of the cathedral and Oudmunster (Old Minster). A study of archival documents sheds light on the cultural and musical environment in Utrecht between 1350 and 1450. It Keywordsts that the cultural life at the time was more sophisticated than hitherto assumed, placing music and music making next to more-investigated cultural branches such as book illumination and silver arts and crafts. Evidence for the performance of polyphony could not be found in the archival documents. However, the rich organ tradition at the most important ecclesiastical institutions, which included the construction and renovation of most state-of-the-art organs and the manufacturing of manuscripts, nevertheless allows for the conclusion that music other than plainchant played an ...