Developmental psychologists have become increasingly interested in how psychophysiological processes relate to adolescent peer functioning. This review discusses advances in the study of the psychophysiology of adolescent peer relations, with a focus on how the autonomic and neuroendocrine systems relate to antisocial behavior, victimization, and peer social status (i.e., dominance, likeability, and popularity). The theoretical and psychological significance assigned to psychophysiological measures is discussed to provide a framework for adolescent peer researchers interested in incorporating these measures into their programs of research. Next, evidence that physiological arousal predicts peer-based behaviors and that experiences with peers may alter the functioning of physiological systems is reviewed. Throughout, the motivational, regulatory, and emotional processes thought to underlie these associations are highlighted. (Contains 4 tables.) [For "Psychophysiology of Adolescent Peer Relations II: Recent Advances and Future Directions," see EJ1012918.]