Coaching is a service that is difficult to evaluate because it is cocreated by clients and coaches in the coaching process and because its results are largely intangible. This makes the task of examining and demonstrating the effectiveness of coaching all the more important and challenging for the profession. This chapter provides an overview of the state of related research. It discusses the questions of whether and how strongly coaching works and how the still low strength of its effects can be improved. The chapter focuses on common and recent methods for evaluating the effectiveness of coaching, which are suitable for scientific research but also for use by coaches for self-evaluating their coaching. On the basis of recent analyses, different short questionnaire scales for clients and coaches are described, whose practical acceptance by clients and coaches has also been demonstrated using large samples. After extensive statistical analyses, separable factors can be recorded economically and reliably.