Medieval prayer books held not only the devotions and meditations of Christianity, but also housed, slipped between pages, sundry notes, reminders, and ephemera, such as pilgrims' badges, sworn oaths, and small painted images. Many of these last items have been classified as manuscript illumination, but Kathryn M. Rudy argues that these pictures should be called, instead, parchment paintings, similar to postcards. In a delightful study identifying this group of images for the first time, Rudy delineates how these objects functioned apart from the books in which they were kept. Whereas...