In 2013, about 10 million adults in the United States had a serious mental illness. The U.S. mental health care system includes a range of federal programs—across multiple agencies— for those with mental illness. Past efforts to develop a list of federal programs supporting individuals with serious mental illness have highlighted the difficulty of identifying such programs. This book identifies the federal programs that support individuals with serious mental illness; the extent to which federal agencies coordinate these programs; and the extent to which federal agencies evaluate such programs. Determining how many people have a mental illness can be difficult, and prevalence estimates vary. While numerous surveys include questions related to mental illness, few provide prevalence estimates of diagnosable mental illness (e.g., major depressive disorder as opposed to feeling depressed, or generalized anxiety disorder as opposed to feeling anxious), and fewer still provide national prevalence estimates of diagnosable mental illness. This book briefly describes the methodology and results of three large surveys that provide national prevalence estimates of diagnosable mental illness.