Did growing literacy in the later medieval period foster popular heresy, or did heresy provide a crucial stimulus to the spread of literacy? Such questions were posed in the polemic of the time - heretics were laici illiterati but were at the same time possessors of dangerous books which their opponents sought to destroy, and among them were preachers whose skills in dialectic and in exegesis threatened orthodoxy - and have challenged the investigators of heresy and literacy ever since. This collaborative volume, written by a group of established scholars from Britain, continental Europe and the United States, considers the importance of the written word among the main pre-Lutheran popular heresies in a wide range of European countries and explores the extent to which heretics' familiarity with books paralleled or exceeded that of their orthodox contemporaries.