The authors outline the three main reasons that developing and implementing effective and cost-efficient intervention services for youth is crucial. An increase in youth crime, committed by youth with multiple problems who have been historically underserved with regard to their mental health and substance abuse service needs has created a situation in which effective interventions are overdue. The article argues the importance of implementing family interventions with an ecological focus. Several such ecological family intervention programs are described, such as the family empowerment intervention (FEI) program, which seeks to improve family functioning by empowering parents. Promising developments in intervention strategies are outlined and include innovations in screening and assessment and service referral. Early intervention services for arrested youth who have been assigned to diversion programs are described, including the programs in operation at the Tampa Juvenile Assessment Center and the Miami-Dade Juvenile Assessment Center. Finally, the article concludes with an overview of the main issues facing service providers who strive to meet the service needs of high-risk youth. Tables, glossary, references