Eighty-five million people were without health insurance coverage at some point between 1996 and 1999, according to a 2002 study supported by The Commonwealth Fund. Instability, or churning, in health plan enrollment was highest among people with low and moderate incomes, as they gained and lost their eligibility for public insurance or moved in and out of private coverage. This project will update estimates of gaps in coverage and churning in insurance enrollment in the United States over the 2004-07 period, to provide policymakers with a baseline for evaluating the capacity of health reform to address the problem. The researchers also will offer solutions for minimizing gaps in coverage that might occur during the implementation of reform.