How does Nietzsche, as psychologist, envision the future of religion and atheism? While there has been no lack of “psychological” studies that have sought to illuminate Nietzsche's philosophy of religion by interpreting his biography, this monograph is the first comprehensive study to approach the topic through the philosopher's own psychological thinking. The author shows how Nietzsche's critical writings on religion, and especially on religious decline and future possibilities, are informed by his psychological thinking about moods. The author furthermore argues that the clarification of this aspect of the philosopher’s work is essential to interpreting some of the most ambiguous words found in his writings; the words that God is dead. Instead of merely denying the existence of God in a way that leaves a melancholic need for religion or a futile search for replacements intact, Nietzsche arguably envisions the possibility of a radical atheism, which is characterized by a mood of joyful doubt. The examination of this vision should be of great interest to scholars of Nietzsche and of the history of philosophy, but also of relevance to all those who take an interest in the interdisciplinary discourse on secularization.