Language is the most essential tool in psychotherapies. Treatment is not possible if there is no common language between therapist and patient. To enable communication between therapists and patients not speaking a common language, the use of professional trained interpreters is inevitable. With the presence of a third person--the interpreter--a triad is established, which bears difficulties, but also chances. In the present paper, these problems and chances are discussed. Recommendations to optimize the work of interpreters in the psychotherapeutic setting are presented. Interpreters should familiarize themselves with the principles of psychotherapeutic methods and clear role concepts for therapists and interpreters should be defined.