In the mid 12th century a “war on heresy” broke out in Europe, leading to “systematic, violent and large-scale repression”. At this time, the church moved away from an “infinitely diverse array of belief and believers” towards specific doctrines regarding heresy. Political and economic preoccupations underscored this move, and Moore casts doubt on the motivations for the persecution that followed. The first part of the book concentrates on the heretical movements and their social significance; the second analyses the how they were suppressed. Moore doubts organised heresy existed and shows how leaders in western Europe came to believe it existed and how it threatened society. The war was waged from above as the ruling elite sought to impose centralised control and their own cultural norms. A convenient combination of paranoia and political advantage? The echoes with the “war on terrorism” in our own time are interesting.