Treatment Improvement Protocols (TIPs), developed by the Center for Substance Abuse Treatment (CSAT), part of the Substance Abuse and Mental Health Services Administration (SAMHSA) within the U.S. Department of Health and Human Services (DHHS), are best-practice guidelines for the treatment of substance use disorders. CSAT draws on the experience and knowledge of clinical, research, and administrative experts to produce the TIPs, which are distributed to a growing number of facilities and individuals across the country. This TIP revises TIP 9, "Assessment and Treatment of Patients with Coexisting Mental Illness and Alcohol and Other Drug Abuse." The main purpose of this TIP is to provide addiction counselors and other practitioners with this state-of-the-art information on the rapidly advancing field of co-occurring substance use and mental disorders. Following a discussion of the evolving field of co-occurring disorders, this document addresses the developments that led to this TIP. It then describes the scope of this TIP (both what is included and what is excluded by design), its intended audience, and the basic approach that has guided the selection of strategies, techniques, and models highlighted in the text. The organization of the TIP is laid out for readers, with the components of each chapter and appendix described in an effort to help users of the TIP quickly locate subject of immediate interest. Chapters in this TIP include: (1) Introduction; (2) Definitions, Terms, and Classification Systems for Co-Occurring Disorders; (3) Keys to Successful Programming; (4) Assessment; (5) Strategies for Working With Clients With Co-Occurring Disorders; (6) Traditional Settings and Models; (7) Special Settings and Specific Populations; (8) A Brief Overview of Specific Mental Disorders and Cross-Cutting Issues; and (9) Substance-Induced Disorders. Appended are: (1) Bibliography; (2) Acronyms; (3) Glossary of Terms; (4) Specific Mental Disorders: Additional Guidance for the Counselor; (5) Emerging Models; (6) Common Medications for Disorders; (7) Screening and Assessment Instruments; (8) Sample Screening Instruments; (9) Selected Sources of Training; (10) Dual Recovery Mutual Self-Help Programs and Other Resources for Consumers and Providers; (11) Confidentiality; (12) Resource Panel; (13) Cultural Competency and Diversity Network Participants; and (14) Field Reviewers. An index is also included. (Contains 53 figures and approximately 750 references.) [This publication was produced by The CDM Group, Inc. for the Substance Abuse and Mental Health Services Administration (SAMHSA), U.S. Department of Health and Human Services (DHHS).]