Dialectic-Behavioral Therapy is a specific psychotherapeutic approach to answer the needs of patients with Borderline Personality Disorder. It uses concepts and techniques of Cognitive Behavioral Therapy and of Humanistic Psychotherapies. For a deeper understanding, it is necessary to include also its Zen-Buddhistic background. The experience of Zen-meditation and the basic philosophy of Zen-Buddhism will be explained. In the context of the historical relation between Zen-Buddhism and Psychotherapy, the position of the DBT will be specified. Finally it will be demonstrated how Zen-Buddhism inspired the practice of DBT and what kinds of problems arise when a modern psychotherapy uses the concept of a premodern conception of the world and human existence.