Medieval literary theory, generated in the educational system and commentary tradition, consisted of systems and conceptual tools for interpreting and communicating the teachings of canonical works. It also offered a range of roles for a writer to adopt or cite for reworking authors (auctores) and authority (auctoritas), as well as materials of lesser prestige. A fascinating hierarchy of literary roles, as variously practised by writers, was delineated by St Bonaventure. This ascended from the humble scribe (a mere copyist), via the compiler (a re-arranger adding nothing of his own) and then the commentator (who ostensibly only explicates the words of the others), to the author, an autonomous asserter who only resorts to the words of others to confirm his own self-styled materials. These roles had considerable implications for Chaucer. This chapter also looks at the terminology for interpreting texts deriving from the academic prologue (accessus) and at different schemes for the understanding of levels of meaning within texts. It closes with a brief mention of the relationship between prescriptive poetics and interpretation in medieval rhetorical tradition.