Borderline personality disorder (BPD) is a severe and complex disorder, historically believed to be ‘untreatable’. This view has been challenged through the success of various therapies in enabling individuals with this diagnosis to create ‘a life worth living’. However despite this progress little is known about how or why these treatments work. This thesis aims to contribute to this understanding through exploring the role of mentalization in BPD. Part 1 is a literature review which critically assesses studies investigating the processes that potentially underlie therapeutic change in BPD treatments. It reveals a lack of any research meeting the criteria for concluding a component of therapy a mechanism of change, but finds evidence for a link between therapeutic alliance and clinical outcome. One suggested explanation for this finding is the development of mentalization within a secure therapeutic relationship. Part 2 is an empirical research paper which further explores the contribution of mentalization to BPD. It investigates whether symptom severity in BPD is associated with performance on a battery of tasks measuring different dimensions of mentalizing ability. It also explores whether the current sample share similar impairments in mentalizing to participants in a previous study (Newbury-Helps,2011) with a diagnosis of antisocial personality disorder (ASPD). The results contradicted hypotheses, finding no evidence for a relationship between BPD severity and mentalizing impairments, and revealing significant differences between mentalizing in BPD and ASPD samples. Possible reasons for these findings are discussed, along with their implications for future clinical practice and research. This study was conducted as part of a joint project (Perera, 2012). Part 3 critically appraises this work. The experience of developing and conducting the thesis is examined and retrospective improvements to the study are suggested, along with ideas for future research, in light of the practical and personal challenges encountered throughout the process
