This book is concerned with the changes in religious thought and institutions from the late eleventh century to the third quarter of the twelfth. It concentrates on monks and nuns, but also takes into consideration hermits, recluses, wandering preachers, crusaders, penitents, and other less organized forms of religious life.

In particular it studies the variety of reform movements, the relation of the reformers to each other and the outside world, and their spirituality and motivation as reflected in their writings and activities.

The work stands in close relation to the author's Three Studies in Medieval Religious and Social Thought (1995), which took what may be called a horizontal approach, studying three topics over the entire Middle Ages. The present work takes a vertical approach, looking at many aspects of reform during a comparatively short period. Together the two works show the relatively rapid change in religious life and sentiments in the twelfth century.