This Health Services Research article by Genevieve Kenney, John Holahan, and Len Nichols investigates the extent to which federal surveys that are regularly used to provide information on health insurance coverage and access to care contain the needed data elements to accurately assess alternative policy options to address the problem of uninsurance. The authors conclude that existing surveys have major data gaps and suggest possible solutions. For example, the content of the Current Population Survey could be modified to deal with current shortcomings in the measurement of insurance coverage. (Health Services Research 41(3): 918-945, 2006.)