In Miserere Mei, Clare Costley King'oo examines the critical importance of the Penitential Psalms in England between the end of the fourteenth and the beginning of the seventeenth century. During this period, the Penitential Psalms inspired an enormous amount of creative and intellectual work: in addition to being copied and illustrated in Books of Hours and other prayer books, they were expounded in commentaries, imitated in vernacular translations and paraphrases, rendered into lyric poetry, and even modified for singing. Miserere Mei explores these numerous transformations in materiality and genre. Combining the resources of close literary analysis with those of the history of the book, it reveals not only that the Penitential Psalms lay at the heart of Reformation-age debates over the nature of repentance, but also, and more significantly, that they constituted a site of theological, political, artistic, and poetic engagement across the many polarities that are often said to separate late medieval from early modern culture.