Noting that the population of foster children who "age out" of the foster care system may be even more at risk than other foster children, this research brief summarizes a longer report examining trends in foster care in the United States, the number and needs of those aging out of the system, and public policy implications. The brief indicates that there has been rapid growth in the population of children in foster care over the past 20 years. Although relatively high exit rates from formal foster care mean that most foster children either return home, go on to live with relatives, or are adopted, a significant number of children remain in the system until they age out. In addition to emotional, behavior, developmental, and health problems related to family and environmental factors, this small population of young adults has a broader constellation of problems that includes emotional disturbance, illegal drug use, and involvement with the legal system, that make adjustment to adult life extremely challenging. The brief offers two strategic goals for public policy: to reduce the number of youth aging out of foster care each year and to help young adults who age out of foster care to overcome the difficulties they may face. The brief concludes by reiterating that helping youth who are aging out of the foster care system to overcome their troubled background remains a pressing societal concern and that research-based information can provide guidance to policymakers and practitioners in their endeavors to provide that assistance. (Contains 47 endnotes.) (KB)