F-Pn fr. 24406 is a codex of 155 folios containing, along with two Old-French prose works and a series of religious lyrics, 301 vernacular songs, all but one with notation. Despite its rich contents, fr. 24406 rarely receives mention in lists of the most important trouvère chansonniers. The majority of its contents are held in common with several of the other twenty chansonniers with notation. Editors consistently prefer other manuscripts’ musical and textual readings to those of fr. 24406, because of the uniqueness of its readings and its supposed inaccuracy. In this thesis, I argue that modern editorial principles have biased scholarship against perceiving what fr. 24406 has to offer and that both its history and its contents are to be valued. Its music scribes, by their very individuality and even their mistakes, reveal much about the notated transmission of the songs, about the previous existence of now-lost sources, and about the craftsmanship displayed by notators of vernacular monophony. I propose to view what has been seen as sloppiness in fr. 24406 as its flexibility. The medieval songbook, sometimes seen as an obstacle to scholarly access to authored originals or to medieval performances, is treated as in itself a worthy work of art. The thesis traces the themes of flexibility and scribal intelligence through the history of fr. 24406. My point of reference is the moment of copying and thus the thesis divides naturally into three parts: before, during and after copying. I begin after, with the combination shelf-mark’s two component manuscripts. The question of their relationship offers an occasion to trace the book’s usage since its compilation and changing scholarly opinions since its first notice. The task of manuscript description is thus largely accomplished through the lens of secondary scholarship. For the manuscript’s prehistory, I mine codicological evidence and apply musical comparison to demonstrate the existence of multiple lost, notated exemplars for fr. 24406. The final part of the thesis is then devoted to describing the notators against this backdrop. Comparison of notational techniques between sources lets us pinpoint the decisions of fr. 24406’s notators and describe their adaptability, their intelligence, and their craft.