This book explores the mind-body issue from both the perspectives of philosophy of mind and philosophy of science. Starting from the problem of mental causation, it provides an overview of the contemporary metaphysical discussion and argues in favour of the token-identity thesis, as the only position that can account for the causal efficacy of the mental. Showing furthermore that this ontological reductionism is not dissociable from epistemological reductionism, the author applies a new strategy of inter-theoretic reduction, which is compatible with the multiple realizability of mental properties. Using functionally defined sub-types, this account establishes a conservative reduction of psychology to neuroscience, which vindicates both the scientific legitimacy and the theoretical indispensability of psychology. This account is illustrated by several empirical examples borrowed from contemporary neuroscience.