This chapter reviews research on coaching effectiveness, examining predictors and outcomes. Despite growing recognition of coaching as a leadership tool, there is no consensus on how effectiveness should be defined or measured. Key predictors include coachee traits (motivation, openness, self-efficacy), coach characteristics (expertise, empathy), and relational/organisational factors (trust, goal clarity). Effectiveness can be evaluated across three domains: individual (self-awareness, confidence, performance), relational (communication, trust), and organisational (leadership pipelines, engagement). Limitations include reliance on self-reports, insufficient focus on team outcomes, and a lack of longitudinal studies. Self-awareness emerges as both a crucial outcome and a mechanism driving effectiveness. The chapter underscores the multidimensional nature of coaching success and provides a framework for evaluating and enhancing its impact within organisational settings.