The success of coaching, which involves professional one-on-one consulting for executives, decision-makers, and self-employed individuals, depends not only on the use of appropriate coaching tools and the consultant's expertise. For coaching to be successful, it is equally important to accurately assess the initial situation and goals of the client, their team, and the entire organization at the beginning of the process. Diagnostic competence and the implementation of systematic diagnostics are now recognized as central factors in coaching. This collection of contributions from recognized experts offers a systematic presentation of diagnostic approaches and levels of analysis in coaching for the first time. In addition to diagnostic approaches from various theoretical backgrounds, such as psychometric, projective, creative, and behavior-oriented methods, relevant levels of analysis are also addressed.