Psychopathy, or psychopathic personality, is a personality construct characterized by impaired empathy and remorse, persistent antisocial behavior, along with bold, disinhibited, and egocentric traits. These traits are often masked by superficial charm and immunity to stress, which create an outward appearance of apparent normality.

Hervey M. Cleckley, an American psychiatrist, influenced the initial diagnostic criteria for antisocial personality reaction/disturbance in the Diagnostic and Statistical Manual of Mental Disorders (DSM), as did American psychologist George E. Partridge. The DSM and International Classification of Diseases (ICD) subsequently introduced the diagnoses of antisocial personality disorder (ASPD) and dissocial personality disorder (DPD) respectively, stating that these diagnoses have been referred to (or include what is referred to) as psychopathy or sociopathy. The creation of ASPD and DPD was driven by the fact that many of the classic traits of psychopathy were impossible to measure objectively. Canadian psychologist Robert D. Hare later re-popularized the construct of psychopathy in criminology with his Psychopathy Checklist.

Although no psychiatric or psychological organization has sanctioned a diagnosis titled "psychopathy", assessments of psychopathic characteristics are widely used in criminal justice settings in some nations and may have important consequences for individuals.^[specify] The study of psychopathy is an active field of research. The term is also used by the general public, popular press, and in fictional portrayals. While the abbreviated term "psycho" is often employed in common usage in general media along with "crazy", "insane", and "mentally ill", there is a categorical difference between psychosis and psychopathy.

Socially, psychopathy typically involves extensive callous and manipulative self-serving behaviors with no regard for others and often is associated with repeated delinquency, crime, and violence. Mentally, impairments in processes related to affect and cognition, particularly socially related mental processes, have also been found. Developmentally, symptoms of psychopathy have been identified in young children with conduct disorder and suggest at least a partial constitutional factor that influences its development.

Disagreement exists over which features should be considered as part of psychopathy, with researchers identifying around 40 traits supposedly indicative of the construct, though the following characteristics are almost universally considered central.

Cooke and Michie (2001) proposed a three-factor model of the Psychopathy Checklist-Revised which has seen widespread application in other measures (e.g., Youth Psychopathic Traits Inventory, Antisocial Process Screening Device).

Cleckley's (1941) original description of psychopathy included the absence of nervousness and neurotic disorders, and later theorists referred to psychopaths as fearless or thick-skinned. While it is often claimed that the PCL-R does not include low anxiety or fearlessness, such features do contribute to the scoring of the Facet 1 (interpersonal) items, mainly through self-assurance, unrealistic optimism, brazenness, and imperturbability. Indeed, while self-report studies have been inconsistent using the two-factor model of the PCL-R, studies which separate Factor 1 into interpersonal and affective facets, more regularly show modest associations between Facet 1 and low anxiety, boldness and fearless dominance (especially items assessing glibness/charm and grandiosity). When both psychopathy and low anxiety/boldness are measured using interviews, both interpersonal and affective facets are both associated with fearlessness and lack of internalizing disorders.

The importance of low anxiety/fearlessness to psychopathy has historically been underscored through behavioral and physiological studies showing diminished responses to threatening stimuli (interpersonal and affective facets both contributing). However, it is not known whether this is reflected in the reduced experience of state fear or where it reflects impaired detection and response to threat-related stimuli. Moreover, such deficits in threat responding are known to be reduced or even abolished when attention is focused on the threatening stimuli.