The substance of this book was delivered in the well-known Rauschenbush Lectures at Colgate-Rochester Divinity School. The author continues the analysis of the current American religious situation which he has probed in earlier books. After contrasting An Age of Belief with An Age of Unbelief, he offers a Christian definition of these key terms, then proceeds, to characterize the modern temper of unbelief as being world-wide, as penetrating many areas of life, and as leading to a reluctance to deal with ""transcendence"". The modern temper is the result of centuries of slow securalization of human existence. Later chapters develop other aspects of Unbelief and Belief, in both their secular and their religious forms. The author draws widely on sources in literature, social science, and theology, and uses a plentitude of quotation. What is sometimes wanting is sharpness of outline, and the impact of the author's own reflection and judgment on the ideas he presents from others.