Toleration of differing religious ideas exists in parts of the contemporary world, but it is still not clear how this came about. Recent work has uncovered the enormous importance one branch of historiography has had in bringing about such tolerance as we have: histories of heresy. This book brings together experts in this field in order to attempt to map out the contours and features of the influence of these histories on early modern and modern conceptions of toleration. Perhaps by showing heretics and heresies to be more benign than once thought, these histories could tease tolerance from the intolerant. The essays in this book attempt to piece together the intentions and effects of key works from this literature in the promotion or rejection of toleration in theory and practice.