What are the effects of certain insurance market reforms that were designed to expand coverage? Researchers at the Urban Institute conducted several analyses looking at the working uninsured and these effects using the Current Population Survey (CPS), the National Survey of America’s Families (NSAF), and the National Health Interview Survey. In particular, they aimed to answer the following five questions: 1) Who are the working uninsured? 2) Why do employer-sponsored coverage rates vary across the 50 states? 3) Have health insurance market reforms affected the composition of insured risk pools? 4) Did HIPAA have any effect in the small group market? and 5) Why do so many workers in large firms lack health insurance? The objective of this series of studies was to provide a better understanding of the working uninsured in order to better inform the policy debate about coverage expansions and identify those interventions most likely to work.