The author, one of the foremost writers in the history of religions, intended this book to be the starting point for those searching for a personal religious experience and begins with an examination of the nature of mystical states and their differentiation from drug-induced states. He proceeds to the question of whether there is religious experience to either state. He offers those impatient with a traditional Christianity alternate routes to explore, by examining Zen, the Upanishads, Huxley, Bonhoeffer, Leary, Jung, Teilhard de Chardin, and commenting upon each with his ascerbic wit. This reprint of the 1972 American edition published by Pantheon contains a new foreword by one of Zaehner's former Oxford students, William L. Newell.