In the completely revised new edition, the two volumes of the first edition are combined into a single work. The first part addresses the fundamentals, taking into account the diagnostic classification systems OPD and DSM. New insights from the Saarbrücken and Innsbruck research groups regarding the therapeutic relationship are formalized in a process model, which precisely explains the nonverbal, particularly affective behavior of the two protagonists as the basis for verbal interventions. This model has proven effective both theoretically and clinically and can be applied for supervision as well as for basic training in all forms of psychotherapy. The author, who has worked for years as a scientific expert in psychotherapy for the Federal Joint Committee for the Evaluation of Healing Procedures, discusses the interface issues in detail.