Volume I of this thesis addresses the adjustment of individuals who have sustained acquired brain injuries. To date there has been a only a thin evidence base for the aetiological factors involved in people's emotional reactivity following what is a profound and potentially devastating life changing event. The first paper critically reviews the concept of 'coping' following an acquired brain injury. This draws on two main bodies of literature. First, Kurt Goldstein's 'organismic theory' and, in particular, the catastrophic reaction model is examined from its phenomenological and existential perspective on adjustment to acquired brain injury. Contemporary developments of the catastrophic reaction model have also been considered. Second, applications of Lazarus and Folkman's stress-appraisal and coping theory to adjustment following injury is reviewed for its more empirically based propositions. A comparison and contrast between the two theories is made. The second paper is a full length research report exploring the subjective nature and frequencies of threat appraisals, and related avoidance coping, reported by people with traumatic brain injury. This goes on to explore the relation of these threat-appraisals, and avoidance coping, to adjustment factors of anxiety, depression and quality of life.