Although relatively few in number-there are only a few hundred thousand members worldwide-the Religious Society of Friends has had an unusually strong impact. Originating in Great Britain in the 17th century, the denomination has since expanded to many other parts of the world while its spiritual influence has reached even further. Concepts such as the "inward light" and "friendly persuasion" are familiar well beyond their own circles and others have often heeded the Quakers' call for cooperation and peaceful resolution of problems as the wisest counsel. Yet, while widely known and admired,...