Assessing the need, use, and developments in mental health/substance abuse care.

This overview presents an introduction to the articles published in this issue of the health care Financing Review, entitled "Mental Health Services and Vulnerable Populations." This article discusses the challenges the mental health and substance abuse (MH/SA) care system is confronted with in terms of equity and efficiency and how the system is responding to these challenges. It further addresses research issues in assessing the need and use of mental health services and summarizes recent activities in the research and evaluation of new delivery and payment systems.