This thesis explores Cognitive Behavioural Therapists’ personal and professional development. Paper one consists of a systematic review of the quality of ten studies examining the measurement properties of CBT Competence Scales (CCSs). Overall the quality of the studies varied, but most were rated as ‘fair’ due to small sample sizes. The review also found inconsistency in the way some measurement properties were defined. The review concluded that more research into the measurement properties of CCSs is needed and that consensus is required to determine appropriate sample sizes and measurement property definitions. Paper 2 explored the personal and professional development of eight students over the course of a postgraduate certificate in Cognitive Behavioural Therapy (CBT), within Personal Construct Theory, using the repertory grid technique. The study found that certificate students perceived an increase in CBT competence but at the expense of interpersonal effectiveness. The study found difference in the personal and professional development of certificate CBT students, compared to previous findings with diploma students. Implications for students, trainers and commissioners are discussed, with suggestions on ways to increase certificate students’ reflection. Paper three presents a critical review of the research process, including both the systematic review and empirical paper. The strengths and limitations will be discussed, as well as the authors personal development as a scientist practitioner as a result of conducting the research.