This chapter is devoted mainly to the late thirteenth-century trouvère manuscript Paris, Bibliothèque Nationale MS jr. no. 846 (known by standard abbreviation as MS O and known also as the “Cangé Chansonnier”), which is unusual for the large quantity of accidentals it contains. Among the 351 songs in this source, 51 have F-sharp signed, and 21 have either C-sharp or E-flat; it is uncommon to find these accidentals in other trouvère sources. The manuscript is distinguished not only by quantity of accidentals but also by the idiosyncratic uses to which they are put. It is unusual in several other respects, including, for one, the arrangement of its contents. Unlike most trouvère anthologies, which feature arrangement by author, MS O is ordered according to alphabetical groups determined by the first letter of the first word of each poem. Within these groups, there is no rigorous order of any kind, though various patterns emerge; for example, songs by Thibaut de Navarre, who is often given pride of place in trouvère anthologies, tend to lead off the alphabetical groups. Therefore it is not surprising that Thibaut's celebrated Ausi cum l'unicorne sui (Ex. 1.1; Beck 1; R 2075; Trouvères-Melodien II: 290) was chosen to be the very first song in the book. Illuminations signal each new alphabetical group in the manuscript, and the illumination that decorates Ausi cum l'unicorne sui strikingly depicts an image from the first stanza of Thibaut's poem, where the narrator proclaims himself to be “like the unicorn, struck with awe when he gazes upon the maiden … so joyful in his torment that, fainting, he falls into her lap; then he is murdered in betrayal.”