The paper first explains five theoretical models of the biological etiology of trauma based on findings from animal and human research. The research data and the models indicate that three key circuits are activated when a person is confronted with a traumatic stressor. First, the preparatory circuit mobilizes the body for an emergency and is influenced by the locus coeruleus and Raphe nucleus which secrete two catecholamines associated with various states of stress. Second, the stress response circuit increases the secretion of the corticotropin-releasing factor and in some cases cortisol. This is one of the main hormones that mobilizes the body to fight or flight. Third, the blunting circuit is regulated by hormones secreted from the opiod-benzodiazopin system. This response blunts the feeling of pain. Disorder behaviors are assumed to arise out of stress/trauma that overwhelms these adaptive systems so they are thrown into states of disregulation via processes of hyposecretion and hypersecretion. Dysregulation occurs in the primary center for the regulation of major life-engaging functions, e.g., sleep, memory, attachment, sexual behavior, aggression, and self-defense. The paper concludes with a brief discussion of the clinical implications of these findings. 12 references