The number of uninsured Americans most often cited in the media severely understates the extent of the health insurance crisis in this country. Annual uninsured counts, which usually include only those who were uninsured when surveyed, exclude the millions more Americans who have coverage now but recently experienced periods without any coverage. Studies sponsored by the Fund and others demonstrate that both the short- and long-term uninsured forgo needed health care and face catastrophic medical costs at rates much higher than people with stable health coverage. Earlier concern that rising unemployment would leave many working families without health insurance sparked interest in ways to help people maintain and fill gaps in their coverage. To inform policy efforts, this project will examine losses and transitions in Americans' health insurance over a four-year period. It will produce new national estimates of the frequency, duration, and causes of long and short periods without insurance. Based on the analysis, the project team will evaluate policy options with the potential to expand health coverage by reducing or eliminating lapses in coverage over time.