How should thought and consciousness be understood within a view of the world as being through-and-through physical? Many philosophers have proposed non-reductive, levels-based positions, according to which the physical domain is fundamental, while thought and consciousness are higher-level processes, dependent on and determined by physical processes. In this book, Kevin Morris's careful philosophical and historical critique shows that it is very difficult to make good metaphysical sense of this idea - notions like supervenience, physical realization, and grounding all fail to articulate a viable non-reductive, levels-based physicalism. Challenging assumptions about the mind-body problem and providing new perspectives on the debate over physicalism, this accessible and comprehensive book will interest scholars working in metaphysics, philosophy of mind, and philosophy of science.