Mordecai M. Kaplan, the founder of the Reconstructionist movement, was the most influential and controversial radical Jewish thinker in the twentieth century. A Modern Heretic and a Traditional Community follows Kaplan from his earliest days as a member in good standing in the Orthodox community, through his period of private estrangement, into his public divorce from Orthodoxy, and ultimately through his many decades as Reconstructionism's leader. Jeffrey S. Gurock and Jacob J. Schacter examine the intellectual influences that moved Kaplan from Orthodoxy and analyze the combination of personal, strategic, and career reasons that kept Kaplan close to Orthodox Jews. More than a biography, A Modern Heretic and a Traditional Community is also a social history of American Orthodoxy and of American Judaism over the last century. Demonstrating how Orthodoxy in America was not a monolithic entity but rather allowed for a wide range of beliefs and practices, the book makes a distinct contribution to the fabric of American social history, Judaism, and the history of religion in the United States.