This chapter provides a developmental perspective on how the US mental health community has responded to periodic requests to define and quantify the need for mental health services in both public and private insurance sectors. It focuses on a model of epidemiological data that will improve the ability to plan for mental health services. The chapter talks about a research enterprise that is attuned to health policy service delivery innovations, service and economic research parameters, and treatment technologies involving both efficacy and effectiveness outcome measurement. Although most managed care systems have been in the private sector, public sector contracts for Medicaid and Medicare mental health services are growing. To be most effective, the role of epidemiology must be inclusive enough to inform us about the unmet need for treatment in the community. Thus, epidemiology may serve as an integrating discipline for basic science, clinical medicine, public health and health policy.