This chapter explores late twelfth- and thirteenth-century texts from theological encyclopaedias to treatises on falconry and cosmetics to argue for more complicated relations in England’s franco-latinate culture than Latin-vernacular binaries. Far from dully derivative didacticism, the large corpus of francophone treatises in this period is an explosion in vernacular poetics and a burgeoning field of experimentation in the forms and modes of knowledge. This argument entails acknowledging the historically situated nature of scientific paradigms and the importance of literary–philosophical textual strategies alongside texts’ social and performative capacities in manifesting knowledge as knowledge. Finally, it is suggested that established francophone knowledge-writing contributes to fresh notions, further developed in later fourteenth-century French and English texts, of narratorial witness as an element of textual authority, whether in instructional or overtly fictional works.