In the 2,000-year history of the Roman Catholic Church, instances of heretical movements have repeatedly challenged the central doctrinal authority of the pope. This critical book explains the construction and beliefs of the organized movements, both large and small, and documents the individuals and their efforts in challenging papal infallibility, singular doctrine, and the Inquisition. It examines how, in spite of Church efforts at maintaining singular control, heretics have never ceased to appear and reappear from ancient times into modern times. This book places heretical movements in their proper context, including how the evolution of cultural and social changes in the Christian world affected how the Church was able to enforce its claimed authority.