This work presents a radically new approach to the mind-body problem, drawing together consideratons from such fields as the philosophy of mind, cognitive science, neurophysiology, relativity and quantum mechanics. The very existence of consciousness, the author argues, poses a challenge to the traditional view of matter, as do the paradoxes of quantum theory. If mind as revealed in introspection, matter as manifested in observation and experiment, are to be seen as dual aspects of a unitary underlying reality, then a fundamental adjustment is called for in our understanding of mental and physical phenomena alike. The book demonstrates the need for a conception that is rooted both in the latest thinking about the foundations of quantum mechanics and in some previously neglected ideas of Bertrand Russell. Its implications are far-reaching and startlingly at odds with the conventional way of looking at the world and at the place of mind within it.