Some experiences of the natural world bring a sense of unity, knowledge, self-transcendence, eternity, light, and love. This is the first detailed study of these intriguing phenomena. Paul Marshall explores the circumstances, characteristics, and after-effects of this important but relatively neglected type of mystical experience, and critiques explanations that range from the spiritual and metaphysical to the psychoanalytic, contextual, and neuropsychological. The theorists discussed include R. M. Bucke, Edward Carpenter, W. R. Inge, Evelyn Underhill, Rudolf Otto, Sigmund Freud, Aldous Huxley, R. C. Zaehner, W. T. Stace, Steven Katz, and Robert Forman, as well as contemporary neuroscientists. The book makes a significant contribution to current debates about the nature of mystical experience.