In the United States, Medicaid is a government program that provides health insurance for 85 million individuals (adults and children) with limited income and resources. The program is partially funded and primarily managed by state governments, which also have wide latitude in determining eligibility and benefits, but the federal government sets baseline standards for state Medicaid programs and provides a significant portion of their funding.

In most states, anyone with income up to 138% of the federal poverty line qualifies for Medicaid coverage under the provisions of the Affordable Care Act. A 2012 Supreme Court decision established that states may continue to use pre-ACA Medicaid eligibility standards and receive previously established levels of federal Medicaid funding; in states that make that choice, income limits may be significantly lower, and able-bodied adults may not be eligible for Medicaid at all.

Medicaid is the largest source of funding for medical and health-related services for people with low income in the United States, providing free health insurance to 74 million low-income and disabled people (23% of Americans) as of 2017, as well as paying for half of all U.S. births in 2019. As of 2017, the total annual cost of Medicaid was just over $600 billion, of which the federal government contributed $375 billion and states an additional $230 billion. States are not required to participate in the program, although all have since 1982. In general, Medicaid recipients must be U.S. citizens or qualified non-citizens, and may include low-income adults, their children, and people with certain disabilities. As of 2022 45% of those receiving Medicaid or CHIP were children.

Medicaid covers healthcare costs for people with low incomes, while Medicare is a universal program providing health coverage for the elderly. Medicaid offers elder care benefits not normally covered by Medicare, including nursing home care and personal care services. There are also dual health plans for people who have both Medicaid and Medicare. Along with Medicare, Tricare, and ChampVA, Medicaid is one of the four government-sponsored medical insurance programs in the United States. The U.S. Centers for Medicare & Medicaid Services in Baltimore, Maryland provides federal oversight.

Research shows that existence of the Medicaid program improves health outcomes, health insurance coverage, access to health care, and recipients' financial security and provides economic benefits to states and health providers.