Posttraumatic stress disorder (PTSD) is one of the few psychiatric conditions where a specific psychosocial stressor is explicitly tied to etiology. Although a majority of people experience a traumatic event in their life, most of them will not develop PTSD or other mental health problems such as depressive or anxiety disorders. Emotional and neurobiological responses to psychosocial stressors show striking individual variation. In this paper cognitive appraisal and coping factors are explored as potential sources of individual differences in the neuroendocrinological stress response, and subsequently in mental health outcome. Continued study of the psychobiology of trauma and PTSD will enhance our understanding of adaptation to psychosocial stressors and support efforts to treat associated psychological and biological sequelae.