“Mental Content” systematically investigates the relationship between the nature of mental states and the world in which these states exist. It examines the opposing theses of internalism and externalism: internalism takes the contents of the mind to be essentially independent of the surrounding world, while externalism supposes there to be a deep connection between states of mind and conditions in the nonmental world. Is the mind fundamentally autonomous with respect to the world, or does the world enter into the very nature of the mind? A qualified externalism is defended. “Mental Content” proposes significant advances in the disputes about mind and brain, personhood, perception, scepticism, folk psychology and the mechanism of mental representation.