This thesis is written as three chapters detailing five studies related to the coaching of psychological skills (PS) and coach behaviour change. There were three main aims to this thesis: (a) to utilise a rigorous approach to the implementation and evaluation of a sport psychology intervention, guided by Medical Research Council guidelines for complex interventions; (b) to extend know ledge regarding the effective facilitation of coach behaviour change; and (c) to establish an effective fo1mat of coach intervention to optimise coach provision of PS support for athletes. Study 1 piloted a need supportive coaching PS intervention informed by Self Dete1mination Theory (Ryan & Deci, 2002). The mixed method intervention evaluation demonstrated positive outcomes in the coach encouragement of PS, some athletes' use of PS and some athletes' training behaviours. Additionally, unintended outcomes were also evident ( e.g., changes of coach employment and further dissemination regarding PS). The process evaluation of the pilot study highlighted that the intervention was need supportive. Possible improvements were identified for future interventions in terms of the provision of structure, the measurement of behaviour change and data collection processes. Based on the pilot findings an intervention process model was created to indicate the components of coach change to be addressed in the subsequent intervention; namely, coach understanding of PS, coach need satisfaction, coach self-discrepancies, coach attitudes, coach intentions to coach PS and coach procedural knowledge. Studies 2-4 involved the development of novel coaching PS measures. Specifically a questionnaire measuring the fundamental components of coaching PS (CPS-F) and a questionnaire measuring the need supportive coaching of PS (CPS-NS) were developed. Following confirmatory factor analysis procedures and item deletion, acceptable model fits were provided for each measure, supporting a 3-factor structure for the CPS-F and a single factor structure for the CPS-NS questionnaires. Study 4 provided initial support for the concu1Tent, discriminant and predictive validity of these questionnaires. Study 5 was a full-scale intervention implementation and evaluation informed by Study 1 and using measures created and validated in Studies 2-4. The study used a mixed-methods between-groups design to compare the efficacy of standardised PS workshops delivered online and a need-suppo11ive coaching PS mentoring intervention. The results revealed that the mentoring intervention had more positive, long-term impact on the coaching of PS and athlete awareness of PS use than the workshop method. However, the coaches who received the online intervention did experience some need support which was an unintended consequence. It was revealed that the relationship between the coaching of PS and athletes' performance is mediated by athlete awareness of PS, athlete use of PS in training and athlete training behaviour ( coping and effort). Levels of need suppo11 provided on the programme were related to coach need satisfaction, coach beliefs about PS and coach intentions to coach PS highlighting that future interventions should seek to better support coaches' needs. At the end of thesis a publication plan of how the PhD chapters were to be published has been provided (See Appendix L).