For the third edition, this comprehensive history of the great heretical movements of the Middle Ages has been updated to take account of recent research in the field.

Malcolm Lambert was Reader in Medieval History at the University of Bristol until 1991 when he retired to devote himself to writing and research. His previous books are Franciscan Poverty (1961, reissued 1998) and The Cathars (paperback edition, 1998). He is now working on a history of the Conversion of Britain.