Executive Summary Improving Health Services Research on Uninsurance and Underinsurance One of the dominant health policy issues over the past three decades has been expanding access to health insurance for non-elderly Americans. As of March, 2008, there were 47 million uninsured Americans, and millions more are identified as “underinsured.” In this essay, I address the key research questions surrounding access to health care for the uninsured and underinsured. The first is developing a richer understanding of why individuals are uninsured: how do we define the level at which the uninsured can afford insurance, and how do we separate affordability from other reasons for a lack of insurance coverage. The second is a broad understanding of the personal and social implications of uninsurance, moving beyond health outcomes to look at measures of psychological and financial stress and social implications through the labor market. The third is defining and understanding the implications of “underinsurance,” particularly relative to the problem of the uninsured. Finally, in the last section I tackle the issue of how to improve research in these areas to address these important unanswered questions.