Opinion regarding the involvement of the therapist as a person in the treatment of patients has changed during the past century. Freud’s “blank-screen” approach, in which the therapist is not personally involved in the analysis of the patient’s problems, has been replaced by an approach which recognizes that the therapist is part of the treatment in a personal way, albeit within professional boundaries. In psychotherapeutic thinking, this is seen as a paradigm shift from a one-person psychology to a two-person psychology. When an interpreter mediates the communication between therapist and patient, a third person becomes involved in the relationship. Examples from empirical research have shown that therapists, patients, and interpreters act according to the principles of a three-person psychology. This paper argues that the strict “neutrality” that is part of most codes of conduct for interpreters should be redefined, taking these findings into account.