Conscious experience presents a deep puzzle. On the one hand, a fairly robust materialism must be true in order to explain how it is that conscious events causally interact with non-conscious, physical events. On the other hand, we cannot explain how physical phenomena give rise to conscious experience. In this wide-ranging study, Joseph Levine explores both sides of the mind-body dilemma, presenting the first book-length treatment of his highly influential ideas on the "explanatory gap," the fact that we can't explain the nature of phenomenal experience in terms of its physical realization. He presents a careful argument that there is such a gap, and after providing intriguing analyses of virtually all existing theories of consciousness, shows that recent attempts to close it fall short of the mark. Levine concludes that in the foreseeable future consciousness will remain a mystery.