Current scholarship conceives of medieval society as remote, existing in the chronological and intellectual space of the pre-modern and thus, categorically other. In the study of literature, this enforced alterity takes form as an assertion of conceptual difference in the ontological status of literature. Medieval literary criticism, as current scholarship holds, had no concept of 'literature' as we understand it; rather, literary works were considered to pertain to the study of ethics. Under this hermeneutic rubric, medieval readers would seek moral instruction in their poetry; fictional narrative and literary style were integumenta concealing an ethical truth which was to be identified and clearly explicated.This dissertation addresses marginalia that suggest another set of reading practices entirely. Latin marginalia in the manuscripts of Chaucer's poetry reveal an affinity not for delineating orthodox interpretation, but rather for creating—and reveling in—intertextual hermeneutic ambiguity that diverges more from ethical reading practices than current scholarship has allowed. Yet the glosses have never been properly understood or integrated into the study of the poet's works, despite the fact that the scholars who have most closely studied these manuscripts believe the glosses to be the work of Chaucer himself. This dissertation begins from a consideration of the authorial glosses in Troilus and Criseyde and The Canterbury Tales which engage readers at multiple levels of literacy, enabling, for certain tiers of readers, the proliferation of multiple competing interpretations of the text. I trace the glosses' evolution through their adaptation by readers the 15th century. Before turning to a case study of a series of readers' glosses to Troilus and Criseyde, which highlight a new emphasis affective methods of reading—typically only addressed in devotional literature—in which readers engage in emotional identification with, and absorption into, their texts. It concludes by addressing potential analogues—both in England and on the continent—arguing that these manuscripts further affirm the hermeneutic of the Chaucer glosses. Reading Chaucer's poetry as it was circulated in medieval England, accompanied by its marginal apparatus, significantly reshapes modern critical approaches to Chaucer's poetry in particular and to medieval critical practices in general.