I begin by giving an outline sketch of the psychopathic personality and setting out the central problem of the book: how should we respond to such a person and their actions, either at an interpersonal or a societal level? Should we blame or praise them, or hold other reactive attitudes towards them such as resentment or indignation, or should we treat them ‘objectively’, as a problem to be solved? If psychopaths are to be punished by society, could this be on the basis of desert and retribution, or only of considerations such as deterrence or the prevention of harm? In short, are they morally responsible? I consider and then reject a suggestion that this question can be settled a priori, based on the idea that conclusions based on psychopaths’ behaviour cannot without circularity be used to explain that behaviour. I then sketch the central argument of the book: 1. A person cannot be held responsible for failing to act on reasons that she is unable to recognise as reasons. 2. Psychopaths are unable to recognise reasons for action stemming from the interests, needs and concerns of others. 3. Hence, they are not responsible for failing to act on them.