The mind-body problem is in fact a cluster of closely related problems. The most vexing problems it would seem involve conscious experience. What are qualia the variegated raw feels of conscious experiences? Do they take part in the causal goings-on of the physical world? Do they make a difference? And if so can we give a scientifically plausible account of their causal relevance? It is my contention that qualia are neurophysiological properties of the organisms that have them. Not only elegant and parsimonious such an account provides for a straightforward explanation of the causal efficacy of conscious experiences. If qualia are neurophysiological properties of the central nervous system their place in the dynamical economy of the living organism-and thus the natural world-is apparent and unproblematic. However the identity thesis faces a number of substantive objections and it is the aim of this book to evaluate its prospects in the face of these challenges.