Antisocial personality disorder (ASPD or infrequently APD) is a personality disorder characterized by a long-term pattern of disregard of, or violation of, the rights of others as well as a difficulty sustaining long-term relationships. Lack of empathy and a contemptuous attitude are often apparent, as well as a history of rule-breaking that can sometimes include law-breaking, a tendency towards chronic boredom and substance abuse, and impulsive and aggressive behavior. Antisocial behaviors often have their onset before the age of 8, and in nearly 80% of ASPD cases, the subject will develop their first symptoms by age 11. The prevalence of ASPD peaks in people age 24 to 44 years old, and often decreases in people age 45 to 64 years. In the United States, the rate of antisocial personality disorder in the general population is estimated between 0.5 and 3.5 percent. In a study, a random sampling of 320 newly incarcerated offenders found ASPD was present in over 35 percent of those surveyed. One out of 17 (6 %) of divorces involves a person affected by ASPD.

Personality disorders are a class of mental disorders characterized by enduring and inflexible maladaptive patterns of behavior, cognition, and inner experience, exhibited across many contexts and deviating from those accepted by any culture. These patterns develop by early adulthood, and are associated with significant distress or impairment. Criteria for diagnosing personality disorders are listed in the fifth chapter of the International Classification of Diseases (ICD) and in the American Psychiatric Association's Diagnostic and Statistical Manual of Mental Disorders (DSM).

The equivalent concept of dissocial personality disorder (DPD) is defined in the International Statistical Classification of Diseases and Related Health Problems (ICD); the primary theoretical distinction between the two is that antisocial personality disorder focuses on observable behaviours, while dissocial personality disorder focuses on affective deficits. Otherwise, both manuals provide similar criteria for diagnosing the disorder. Both have also stated that their diagnoses have been referred to, or include what is referred to, as psychopathy or sociopathy. However, some researchers have drawn distinctions between the concepts of antisocial personality disorder and psychopathy, with many researchers arguing that psychopathy is a disorder that overlaps with but is distinguishable from ASPD.