The purpose of the Substance Abuse and Mental Health Services Administration's Center for Substance Abuse Treatment's (CSAT's) Cannabis Youth Treatment (CYT) Project Cooperative Agreement was to test the relative effectiveness and cost-effectiveness of a variety of interventions designed to eliminate marijuana use and associated problems in adolescents and to provide validated models of these interventions to the treatment field. The target population was adolescents with cannabis use disorders of abuse or dependence, as defined by the American Psychiatric Association (1994), who were assessed as appropriate for treatment in outpatient settings. This manual guides therapists and their supervisors in using the multidimensional family therapy intervention with adolescents and their caregivers. Multidimensional family therapy is the multisystemic family-focused treatment described in this manual for experienced family therapists that includes 12 weeks of in-clinic and telephone sessions working with individual adolescents and their families. MDFT targets the psychosocial functioning of individual family members, the family members' relationships, and influential social systems outside the family. The approach strives for consistency and a coherent and logical connection among its theory, principles of intervention, and intervention strategies and methods. The intervention methods derive from target population characteristics, and they are guided by research-based knowledge about dysfunctional and normal adolescent and family development. Interventions work within the multiple ecologies of adolescent development, and they target the processes known to produce and/or maintain drug taking and related problem behaviors. Appendixes include key terms and abbreviations, administrative issues in implementing MDFT, a summary of the MDFT research program, and a detailed account of the CYT study. (Contains 265 references.) (GCP)