This is the first comprehensive account in English of the most feared and the most mysterious of medieval heretics. A crusade was launched to uproot them in the south of France, the Inquisition was developed to suppress them, and St Dominic founded his friars to preach against them. Their history and that of the medieval Church are inextricably mingled. This book puts the Cathars back into the context where they belong - that of medieval Catholicism. It studies the rise and fall of the heresy from the twelfth-century Rhineland to fifteenth-century Bosnia and the Church's counteraction, peaceful and violent.Within the exposition, Italian Cathars are given their rightful place, a chapter is devoted to the puzzle of the Bosnian Church, and perspective is given to Le Roy Ladurie's brilliant but wayward Montaillou. A final survey assesses the legacy of a heresy which still exerts its strange fascination. This book combines scholarly investigation with lucid narrative. It is, in short, historical writing at its best and likely to become the definitive account of a subject of enduring interest and importance.