Psychopathy has been defined from categorical, dimensional, and behavioral perspectives. The categorical approach presumes that some people are psychopathic while others are not. The dimensional approach considers psychopathy as the extreme manifestation of a personality continuum. Both the categorical and the dimensional approaches define psychopathy in terms of personality characteristics. The behavioral approach, on the other hand, defines psychopathy as the presence of a specific pattern of antisocial, irresponsible behavior, with psychopaths being those who engage in such behavior. The description of people as aggressive, impulsive, egocentric, and irresponsible appears to identify a type of person for whom predictions of antisocial behavior tend to be accurate, making it reasonable to treat psychopathy as a legitimate personality description, one for which a categorical definition is suitable. Theories about stages of moral development have provided one basis for considering the psychopath immature. Empirical evidence has not supported these theories, and the concept that moral judgments can rest on maturational processes is fundamentally incorrect. Recent studies of psychopaths have identified two other characteristics that bear on their moral development: their relative immunity to the deterrent effects of punishment and their attraction to new experiences. Various studies have sought to posit these characteristics in biological factors, but these have yielded only clues that fail to solve the mystery. Much the same can be said of the search for social causes. Although both parental rejections and inconsistent punitiveness have been implicated in the etiology of psychopathy, it has not been established that such parental patterns precede psychopathic characteristics. Sixty-one references are provided.