Traumatic brain injury (TBI) is a leading cause of cause of disability in Australia, and is associated with substantial personal, social and economic burden. Emotion-related difficulties represent a major cause of disability following brain injury, often over and above that of physical impairment. Furthermore, emotional disorders are particularly common post-TBI, with higher prevalence rates than within the general population. Despite this, there is a paucity of research supporting evidence-based psychotherapeutic interventions for depression and anxiety post-TBI. As such, an enhanced understanding of emotional adjustment post-TBI is vital, to guide development of effective interventions for this population. Over the last decade clinicians and researchers have been promoting a transdiagnostic approach to understanding depression and anxiety within the general clinical population. The transdiagnostic approach endeavours to understand and/or treat processes associated with multiple psychological disorders, with the aim of developing more parsimonious conceptualisations of psychopathology. Advocates of the transdiagnostic approach suggest that there are common underlying factors across anxiety and depression, and that these disorders may be part of the same fundamental emotional syndrome. This viewpoint may be highly relevant to the TBI population, as psychological distress post-TBI often presents as a range of neurobehavioural and emotional reactions, rarely fitting neatly into a diagnostic category. Therefore, a transdiagnostic approach may offer an enhanced understanding of the factors which underlie depression and anxiety following TBI. As such, the broad objective of this thesis was to develop a preliminary working transdiagnostic model of psychological distress for individuals one year or more post-TBI.