This paper reviews the psychophysiological literature related to violent behaviors. It explores the interactions of environmental influences, pain, stressors, hormones, and neurotransmitters. It presents ways in which maltreatment in the form of abuse or neglect exacerbates preexisting psychobiological vulnerabilities. It proposes that whatever forces increase impulsivity and irritability, engender hypervigilence and paranoia, diminish judgment and verbal competence, and curtail the recognition of pain in the self and others, will enhance violence, and presents evidence that maltreatment has all of these effects.