Psychopathy refers to the personality disposition to charm, manipulate, and ruthlessly exploit other persons. Psychopathic persons are lacking in conscience and feeling for others; they selfishly take what they want and do as they please without the slightest sense of guilt or regret. Psychopathy is among the oldest and arguably the most heavily researched, well-validated, and well-established personality disorder. Yet it has only indirect, informal entry in the DSMs. This chapter discusses traditional alternative conceptualizations of psychopathy, emphasizing in particular the influential and heavily researched Psychopathy Checklist-Revised. Discussed as well is the existing research concerning the epidemiology, etiology, course, treatment, and biological aspects of psychopathy, as well as its implications for DSM-5.