Health insurance in the United States continues to be a complex mix of private and public programs. The advent of health-care reform legislation, the Patient Protection and Accountable Care Act (PPACA), portends significant new challenges and research opportunities. This chapter provides a historical overview of the US system and a summary of the key features of the PPACA that affect health insurance. Attention is then directed to the key issues in health insurance and an update on the research undertaken in the last decade. Key topics include adverse selection and moral hazard where the new research examines multidimensional selection, forward-looking behavior, prescription drug coverage, and utilization management as a mechanism to control moral hazard. Managed care continues to be the dominate form of private coverage and the research on its comparative advantage in selective contracting is reviewed along with the evidence on managed care backlash and the efforts at provider consolidation. New research is beginning to examine the market structure, conduct, and performance of the health insurance sector and this is reviewed. Much of the chapter is devoted to new research on important aspects of employer-sponsored health insurance. This includes premium sensitivity, compensating wage differentials, and the tax treatment of employer-sponsored coverage. Significant new research has also examined the role of the employer as agent for his/her workers. Individual, non-group markets have historically played a minor role in the USA. Knowledge of these markets is reviewed as is the immerging market in high-deductible health plans. Early research on state insurance regulation typically found only small effects. More recent research has tended to examine the effects of specific laws and to explore the effects among high- and low-risk individuals and firms. Finally, there has been substantial new research focusing in the Medicare program for older residents. This work examines the effects of risk adjustment in the Medicare Advantage program and the effects in the Medicare prescription drug program. Throughout the chapter attention is given to future avenues of research that are likely to emerge from the PPACA legislation.