It is only recently that neurologists, psychiatrists, psychologists, and physiatrists came to the realization that emotional dysfunction, not cognitive dysfunction, is the more common cause of persistent post-concussive disability. That awareness happens to coincide with something of a renaissance in the understanding of the neurobiology of emotion which challenges the nineteenth- to twentieth-century classifications. Rather than a simplistic model classifying feelings as positive or negative, attention has swung toward the study of emotional regulation as a multifaceted and ever- dynamic homeostatic function of the organism. Concussive brain injury is not diffuse in the sense of equally distributed. Instead, and unfortunately for survivors of CBI, concussion tends to cause disproportionate harm to several cortical and subcortical regions that are critical for emotional regulation. Indeed, a striking overlap characterizes the features -- and frequently the occurrence -- of CBI and so-called Post Traumatic Stress Disorder (PTSD). This chapter will attempt to clarify how an evolved concept of mood and stress helps account for the commonplace observation of lasting, yet highly individually variable, post-CBI psychic distress.