<p>Psychophysiological reactivity has been a critical emphasis in the quest to understand the underlying mechanisms of psychopathy. The combination of reduced affective responding and antisocial behavior in psychopathy sparked questions that called for a structured assessment of the features of this condition – a need that Robert D. Hare addressed through his development of the Psychopathy Checklist, which became the focus of extensive research into autonomic and central nervous system activity and reactivity. This paper reviews the impact of Hare’s initial work on subsequent research which aims at understanding the role of physiological processes in psychopathy and related psychopathic traits as a neurodevelopmental disorder, as somatic aphasia, and as a condition of low fear reactivity and resistance to external stressors, in successful as well as unsuccessful psychopathy. Avenues for future research highlighted by this review include the consideration of developmental trajectories across measures and in relation to the different facets of psychopathy.</p>