The Confessio Amantis, a poem completed in 1393, opens with its author's pledge to: wryte of newe som matiere essampled of these olde wyse [write anew some matter modeled on these old wise books]. Expressing a commonplace among writers of vernacular literature in late medieval England, John Gower describes authorial activity as the process of translating and assimilating pre-existing narratives. This dissertation argues that such conceptualizations of authorship were embraced by illuminators of vernacular literature in their burgeoning notion of invention before the ascendance of print: as translation and compilation provided a model of creativity founded on the alteration of models, illuminators located an ideal congenial to both the restrictions and freedoms of their own profession. The centerpiece of the study is Pierpont Morgan MS M. 126, a manuscript of the Confessio Amantis produced c.1472 and made for Edward IV and his Queen Consort, Elizabeth Woodville. Although it has been acclaimed as one of the most impressive extant manuscripts of Middle English literature, it has never been the subject of a major study. The aim of the dissertation is to recognize and restore to the illustrator the power of his position between the conception of a text and the consumption of a book. Part One focuses on the illustrator's interactions with the textual voices of the Confessio Amantis, demonstrating how the images in nineteen manuscripts of the poem, including the Morgan Confessio, address the identity of the author of the poem (Chapter One); and how miniatures in the Morgan Confessio reinterpret its Ovidian narratives (Chapter Two). Part Two shifts attention to the illustrator's confrontation with his patrons. Although their impact on the production of this manuscript appears to have been minimal, I observe how, as patrons they furnished a visual context for the Morgan Confessio from within their own library of illustrated historical manuscripts (Chapter Three) and books on science (Chapter Four). Produced just before Caxton printed his first book in Westminster in 1476 and standing at the threshold of standardization, this manuscript offers a complex glimpse into the variance that epitomized creative activity in illustrated vernacular manuscripts.