After providing an overview of drug treatment as a crime- control measure, the paper identifies the typical barriers to offenders receiving treatment. This is followed by a description of the core components of the seamless system of care, particularly for transition services. Under this system, offenders are assessed in terms of severity of drug use and propensity to commit crimes, and treatment placement is made accordingly. Treatment contains an intensive component, followed by less intensive treatment and then aftercare; the most effective treatment process is 12 months of care. Supervision and monitoring of the requirements are critical to improving treatment outcomes. External means, including face-to-face interviews, curfews, electronic monitoring, and day reporting, are used to control the offender in treatment and supervision programs. Sanctions or compliance monitoring are used to deter clients from further drug use; drug testing is crucial in monitoring drug use and deterring offenders from further involvement in drugs. The systemic case management approach integrates the aforementioned system features within the criminal justice and treatment systems as part of the ongoing processes for managing offenders. The final section of this paper presents 12 principles for effective systems of care that focus on transitional policies and treatment retention. 5 exhibits and 91 references