“Rewrite this Book” argues that medieval English bookmakers created bound works with aggregate and varied contents akin to earlier compilations and compendia. These objects, which I call “mixed-manuscripts” are often anonymously produced, contain many works by different writers and in different genres, serve as the material grounds for associative reading not directed by a compiler’s notes or evaluations, and are fertile ground for associative thought and creative production. These mixed objects were constructed by hand both by amateurs and professionals to protect, collect, and associate texts with each other, forming textual ‘societies’ between the covers of a book. Within these books, clusters of regularly associated medieval texts began to circulate in small, stable groups of ‘textual companions,’ appear together in several different manuscripts. Some late medieval poetry, Piers Plowman chief among them, took these mixed structures as a compositional model and crafted intricately associative poetical works rooted in companion networks.Chapter one reads the Vernon manuscript as a mixed-manuscript which contains “Ypotis” and the Middle English “Castle of Love” which together present Christian political thought in vernacular poetry, giving its lay audience an idealized fantasy of political harmony. Chapter two reads across Piers Plowman from the Peace in Passus 4 to the Peace in 18 and unites them allegorically to picture of ‘peace’ personifying across gender, social position, and poetic space. Adapting Grosseteste’s Castle into later versions of Piers Plowman produces an unsteady instantiation of the concept which reveals difference in ‘peace’ afforded to the farmer-Peace of passus 4 and that brought about by the noble daughter of the king in passus 18. Chapter three examines the conversation between Meed and Conscience, the episode of the Pardon, and Imaginatif’s bookish suggestions as examples of allegorizations trying to cope with the textual complications of the poem’s expansion via integration of external texts. Chapter four argues that boke of John Colyns, which contains early versions of John Skelton’s poetry alongside the established stanzaic Morte Arthur, radicalizes Morte with Skelton verse and protects the same through its association with the politically dull Morte. Colyns thus imagines that his boke is destined to make Skelton great, but the laureate updates and collects his poems in print, authorizing himself for fame and political security.