This article examines the efforts of Matthew Parker and his scholarly circle to understand the medieval books that he collected as archbishop of Canterbury. It argues that Parker made sense of his books by connecting them to what amounted to an emerging history of the book. That is, Parker began to piece together the formal features of different medieval books into a rough but increasingly refined timeline of the history of book production in order to contextualize any given manuscript. The evidence can be found scattered throughout Parker's library, in the form of annotations, transcripts of passages, copied illustrations, and printed books that offer a wealth of information about how Parker's team understood the books they handled. This documentation reveals how they combined scribal knowledge with textual information, to powerful ends. By connecting Parker's practices to contemporary developments in other areas of knowledge production, from alchemy to conjectural emendation, this article offers a new way forward for scholarly analysis of the early modern study of older books, especially for our analysis of early modern practices and paradigms that do not fit modern definitions of paleography and codicology.