The Tongeren collection of manuscripts is an exceptional collection of Gregorian manuscripts with numerous chants from the local repertoire. They also document the radical liturgical reform of Radulphus de Rivo, a Tongeren humanist from the fourteenth century. The exceptional value only becomes clear when one compares with similar books from other collegiate churches. The Tongeren book is not only much more extensive but also more detailed about the performance prosecution of the hymns. The manuscripts are also extremely valuable from a historical point of view as they contain two types of notation which is unique to Flemish Gregorian manuscripts. Finally, the collection is the only music library of a collegiate church that is simultaneously extensively homogeneous and in situ preserved.