This 24-hour course summarizes treatment of COD in the substance abuse and mental health fields. It contains chapters on terminology, assessment, and treatment strategies and models, as well as recommendations for treatment, research, and policy planning. The primary concern of this course is co-occurring substance use (abuse and dependence) and mental disorders, even though it is recognized that this same vulnerable population is also subject to many other physical and social ills. The information in this course synthesizes knowledge and grounds it in the practical realities of clinical cases and real situations so the reader will come away with increased knowledge, encouragement, and resourcefulness in working with clients with co-occurring disorders. The course includes important work on nicotine dependence, an important cross-cutting issue. This course is based upon TIP 42 – Substance Abuse Treatment for Persons with Co-Occurring Disorders.