This portfolio thesis has three parts: a systematic literature review, an empirical report and supporting appendices. Part One: A systematic literature review in which empirical papers utilising Acceptance and Commitment Therapy for people with neurological conditions and acquired brain injuries are reviewed for effectiveness for psychological flexibility and wellbeing. A systematic database search identified sixteen studies to be reviewed. Methodological considerations of studies were considered, and their findings were examined using narrative synthesis. Clinical implications and suggestions for future research are discussed. Part Two: An empirical paper combining qualitative and quantitative methodologies to explore the implications of feeling personally responsibility for a brain injury. The quantitative component aimed to examine the relationship between perceived responsibility for injury and shame, and whether self-compassion moderated this relationship. The qualitative data was analysed thematically to explore participants’ experiences of shame, responsibility and self-compassion. The findings are discussed in relation to theory and implications for clinical practice and future research. Part Three: Appendices supporting the systematic literature review and the empirical paper, and a reflective statement on the research process.