Medicaid is the nation's major public financing program for providing health insurance coverage and long-term care services to the poor. This article assesses Medicaid's contributions over the last three decades to improving the coverage, access to care, and health of low-income children and women. The article reviews Medicaid's impact on the low-income population covered by this program, demonstrating both the role insurance plays and its limitations as a strategy for improving the health of vulnerable populations. Medicaid has shown over the last three decades that it is an important lever to help open the door to better health care, and ultimately to improved health for America's poor women and children, by substantially expanding coverage of the low-income population and helping to reduce differentials in access to care between the poor and the privately insured. Gaps in coverage and limitations in access persist, but overall the program has resulted in better coverage, access, and health care for millions of poor children and their parents.