In this paper, we investigate the meaning of "affordability" in the context of health insurance. Assessing the relationship between the affordability of coverage and the large number of uninsured in the U.S. is important for understanding the barriers to purchasing coverage and evaluating the role of policy in reducing the number of uninsured. We propose several definitions of affordability and examine the implications of alternative definitions for estimates of the proportion of uninsured who are unable to afford coverage. We find that, depending on the definition, health insurance was affordable to between one-quarter and three-quarters of the uninsured in the United States in 2000.