Mordecai M. Kaplan, the founder of the Reconstructionist movement, was the most influential and controversial radical Jewish thinker in the twentieth century. This book follows Kaplan from his earliest days as a member the New York Orthodox community, through his period of private estrangement, into his public divorce from Orthodoxy and ultimately through his many decades as reconstructionism's leader. The book is also a social history of American Orthodoxy and American Judaism over the last century.