A clinical consensus has evolved as to the specific areas to be addressed in a comprehensive clinical interview with substance abusers. Knowledge of specific psychopathology and associated comorbidities among addicts will refine this assessment. There are several reasonably reliable and valid objective psychological tests that can be used to provide supplementary information for diagnostic and treatment decisions. Etiological theories, including the disease concept, family systems theory, psychodynamic formulations, and behavioral approaches, have generated treatment interventions of clinical utility. Recent research suggests that psychotherapy, combined with traditional approaches, results in increased therapeutic benefits that were heretofore considered unlikely.