Multisystemic treatment (MST) is based largely on family system conceptualizations of behavior and behavior change, although MST also includes substantive differences from more traditional family systems work. For example, the multisystemic approach views individuals as being nested within a complex of interconnected systems that encompass individual, family, and extrafamilial factors. MST also emphasizes child development variables and often incorporates interventions that are not necessarily systemic, e.g., behavior therapy. An MST approach is described that has a treatment duration of about 30 hours of direct contact over 3 months, a caseload size of four to six families per counselor, and sessions that rarely exceed 90 minutes. In addition, the approach provides services in home and community settings to increase cooperation and enhance generalization. A crucial aspect of the approach is its emphasis on promoting behavior change in the youth's natural environment. It incorporates the family, peers, the school, and court and juvenile services. The importance of training MST practitioners is discussed, as well as the demonstrated cost-effectiveness of the MST approach. 6 references