I read The Formation of a Persecuting Society by this author a few months earlier and liked it quite a lot. The author wrote this book 25 years earlier and it is not nearly as informative. It is a painstakingly detailed account of so-called heretical movements in Christianity in the 11th and 12th centuries, clearly aimed only for professional historians specializing in this period. The author presupposes familiarity with hundreds upon hundreds of persons and events which he mentions in passing without any introduction or overview. Apart from a few brief notes in the concluding chapter, there are no general conclusions or arguments to grab hold of. I would recommend that non-professional historians avoid this early work and read one of his later books instead.