This TIP on the best practice guidelines for treatment of substance abuse aims to help teach treatment providers about the latest information available to design and deliver better services to adolescent clients with substance use disorders. This publication represents advances in the understanding of the immediate and long-term physiologic, behavioral, and social consequences of use, abuse, and dependency. Adolescent substance users differ from adults in many ways, and this TIP explains how knowledge about these differences will help treatment providers grasp why adolescents use substances and how substance use may become an integral part of their identity. A discussion on program design, policies and procedures, and evaluation, as part of program development for treatment, is provided. Other treatment approaches such as therapeutic communities and 12-Step-Based Programs are detailed. It includes a discussion on contemporary family therapy as another effective form of treatment. Youth with distinctive treatment needs are considered in detail, including those in the juvenile justice system; homeless youth; those with nonheterosexual identity; and those with coexisting physical, behavioral, and psychiatric disorders. It concludes with a discussion of the legal and ethical issues of providing treatment to adolescents. The following appendixes are included: "Bibliography,""Medical Management of Drug Intoxication and Withdrawal," and "Field Reviewers." (Contains 11 figures and 173 references.) (JDM)