The present Corpus Troporum volume is a text edition of the Latin liturgical chants called prosulas that embellish the offertory chants of the medieval Roman mass. Up to about 1100 the offertories were sung as an extended chant comprising an antiphon and often several verses. The verses in particular, but sometimes also the antiphons, have an elaborate musical style characterized by long wordless melismas. The melismas received new texts, prosulas, that were incorporated into the offertories. These new texts can be found in manuscripts as early as the tenth century, and the genre continued to flourish until the twelfth century, when prosulas begin to disappear from the sources together with the verses. Only a small number of offertory prosulas appear in later manuscripts. Sofar the majority of the offertory prosulas have not been edited in a modern text edition. The present edition comprises 252 different prosulas related to 84 offertory chants that were sung during the ecclesiastic year. It is notable that a number of prosulas were sung during the cycle of Lent, a time usually deprived of embellishments. The edition is based on 74 manuscripts dating from the tenth to the fourteenth century, the majority being from before 1100 and coming from many different regions of Europe. In addition, the volume offers an introduction and a commentary in French, as well as a table and an overview of the sections in the manuscripts containing the prosulas. The editor is a Latin philologist and a member of the Corpus Troporum research team at Stockholm University.