Psychopathy is a complex higher order personality construct characterized by a constellation of affective, interpersonal and behavioural features, including: egocentricity, deceitfulness and a tendency to manipulate; lack of empathy, guilt and remorse; and a tendency to violate social norms, usually including the criminal law. Psychopathy can be assessed across the lifespan and the construct has been shown to be reliable and valid in a range of clinical and correctional settings. The base rate of psychopathy is low in the general population (0.6%) but significantly higher in criminal justice settings. Research on the developmental origins of psychopathy suggests that social factors and, particularly, adverse upbringing contribute to causation, whilst also establishing its strong biological basis. There is a genetic component and consistent reports of an association between impulsive aggressive traits and dysregulation of the serotonergic system. Imaging studies point to both structural and functional deficits in fronto-temporal circuitry. Psychopathy generally shows a poor response to treatment and is a negative moderator of outcome. There are few well controlled intervention studies but there are suggestions that cognitive skills programmes may be of value. Obstacles to successful psychological treatment include the core personality traits of deceit, manipulation and lack of remorse, as well as general problems of poor motivation, non-compliance and failure to engage in a therapeutic alliance. Future interventions need to target putative proximal causes of psychopathy.