The Middle Ages have long been famous for spectacular forgeries. In this study Alfred Hiatt examines the function of forged documents in late medieval politics and society. In whose interests was it to forge documents? What kinds of narratives were enshrined in forgery? And why did forgery so often escape detection? Both the production and criticism of a range of forgeries are considered, from spurious seventh-century papal bulls of the University of Cambridge, to the Donation of Constantine, and Hiatt argues that the identification of forgeries was no less ideologically motivated than their perpetration. Indeed, medieval forgeries emerge as a fascinating paradox: an illegitimate form of historical writing crucial to the expression of personal, institutional and national identities whose repudiation became central to the formation of modern discourses of authenticity and value.