In this issue we describe a clinical trials study of the impact of adding specific case manager overlay services to "treatment as usual" services for youths in a Juvenile Arbitration Program. In this first article we describe the experimental intervention, the Arbitration Intervention Worker (AIW) service, which was provided to a randomly selected half of the research sample. Our description of the intervention includes an overview of the legal context in which the service was provided, the conceptual foundation for the intervention in Systems Theory, elements of the model emulated in operationalizing the service, phases of the service, issues in staff recruitment and training, and clinical and administrative supervision of AIW case workers. Subsequent articles in this issue describe empirical findings from the clinical trial. (Contains 1 table and 2 notes.)