This book provides the first full single-volume scholarly account in English of the "Waldenses" and examination of the concept of "Waldensianism" from the late 12th century to the Reformation. "Waldenses" is the name given to diverse and widely-scattered groups of religious dissenters since the time of the movement's reputed founder, a rich citizen of Lyon called Valdesius, in the late twelfth century. Though living within the culture of the Catholic Church, these people doubted the holiness of its priesthood and questioned its teachings about the destiny of souls after death. The various strands of this movement emerged and endured over a long period of time. In consequence some earlier historians assumed, rather than demonstrated, that 'Waldensian' heresy remained one coherent phenomenon throughout its life-span. They also tended to neglect some of the transient or 'untypical' aspects of the movement. This new book draws on primary sources to consider each of the manifestations of the movement in turn. It examines connections in space and time through correspondence and tradition between the different groups of Waldenses. It also asks what were the common threads in certain characteristics of religious practice, linking in differing degrees all the forms that the movement took.