The extent to which the surviving sources can demonstrate the cultivation and consumption of the music of the twelfth and thirteenth centuries differs for each of the genres represented in them. Thus although the versions of the so-called Magnus liber organi contained in the three principal ‘Notre-Dame’ sources are sufficiently different to suggest that in a critical edition they should be edited separately, they are similar enough to allow us to infer a certain amount about the origins and cultivation of the music.