Credentialing and privileging are key concepts to understanding how formal professional education and training relate to professional practice. Credentials refer to the diplomas, licenses, and training certificates that have been earned in a particular profession. Privileges are specific diagnostic and treatment procedures that the professional is permitted to perform based upon his/her credentials and experience. In most cases, privileges are related to credentials in a rational manner (e.g., the right to perform brain surgery as a function of a medical degree, a neurosurgery residency, a state license to practice medicine, and board certification). However, in some cases privileges are not rationally given as in the case of psychologists in a clinical setting who are privileged to diagnose and treat but not to admit at a mental hospital. Psychiatrists and psychologists are both experts in the etiology or causes of mental disorders and the wide variety of treatments to address these disorders. Except for such specific privileges as administering psychological tests, electroconvulsive therapy or medication, there is almost a total overlap between the two professions. The privileges of diagnosis, individual, group, marital and family therapy, relaxation and stress management, and hypnotherapy can be administered by all of the mental health professions with proper training in their respective field. The administration and interpretation of psychodiagnostic tests should be restricted to psychologists. None of the other professions provide formal training in this content area. Currently, the American Psychological Association is promoting the development of prescription privileges for psychologists. Several model training programs are investigating appropriate curricula in this area.