The Affordable Care Act (ACA), formally titled the Patient Protection and Affordable Care Act (PPACA), is a United States federal statute signed into law by President Barack Obama on 23 March 2010. It represents the most significant overhaul of the American health insurance system since the creation of Medicare and Medicaid in 1965. The law's primary mechanisms include the expansion of Medicaid eligibility, the creation of regulated insurance marketplaces, mandates and subsidies affecting individuals and employers, and a set of insurance market reforms such as guaranteed issue and prohibition on exclusions for pre-existing conditions.

Prior to the ACA's passage, an estimated 46 to 50 million Americans lacked health insurance coverage.¹⁾ The law drew heavily on earlier proposals from the Heritage Foundation and the Massachusetts health reform law signed by Governor Mitt Romney in 2006, as well as provisions advocated by consumer and labor groups. The legislation passed the Senate on 24 December 2009 and the House on 21 March 2010, with no Republican votes in either chamber. A reconciliation bill, the Health Care and Education Reconciliation Act of 2010, was signed two days later.

The ACA's core provisions include:

• Individual mandate: A requirement that most Americans obtain qualifying health coverage or pay a tax penalty. The Tax Cuts and Jobs Act of 2017 reduced this penalty to $0 beginning in 2019, effectively nullifying the mandate's enforcement.
• Medicaid expansion: States were permitted to extend Medicaid eligibility to adults with incomes up to 138% of the federal poverty level. Following NFIB v. Sebelius (2012), states could opt out; participation varies by state.
• Insurance marketplaces: Federal and state-operated exchanges through which individuals and small businesses may purchase subsidized insurance plans.
• Insurance market reforms: Insurers are prohibited from denying coverage or charging higher premiums based on pre-existing conditions, from imposing lifetime or annual benefit limits, and from charging different rates based on sex. Adult dependents may remain on a parent's plan until age 26.
• Employer mandate: Employers with 50 or more full-time-equivalent employees are required to offer qualifying coverage or pay a penalty.
• Essential Health Benefits: Plans sold in the individual and small-group markets must cover a defined set of benefit categories, including emergency services, maternity care, mental health services, and prescription drugs.

The ACA has faced sustained legal challenges. In NFIB v. Sebelius (2012), the Supreme Court upheld the individual mandate as a valid exercise of Congress's taxing power, while ruling that the federal government could not coerce states into Medicaid expansion by threatening to withdraw existing Medicaid funding.²⁾ In King v. Burwell (2015), the Court upheld the availability of federal subsidies in states using the federally operated exchange.³⁾ In California v. Texas (2021), the Court declined to strike down the remainder of the ACA after the individual mandate penalty was zeroed out, ruling on standing grounds rather than the merits.⁴⁾

Following implementation, the uninsured rate among non-elderly Americans fell from approximately 17.8% in 2010 to 10.0% by 2016.⁵⁾ Debate continues among health economists over the ACA's effects on total health care costs, insurance market stability, labor markets, and the quality and accessibility of care. Proponents credit the law with expanding coverage and consumer protections; critics contend it raised premiums in certain markets, distorted labor incentives, and increased federal spending. These competing assessments are addressed on the Debate page.

Most health policy researchers agree that the ACA substantially reduced the number of uninsured Americans. There is no comparable consensus on its effects on aggregate health outcomes, long-run costs, or market structure; these remain active areas of empirical and normative dispute. See the Health Policy Consensus page for the scope and limits of existing agreement.

• Government Expansion Viewpoint: The ACA represents an appropriate use of federal authority to correct market failures in health insurance and to establish a floor of access to care.
• Market Reform Viewpoint: The law's mandates and regulations distort insurance markets, reduce consumer choice, and expand federal control over a sector better governed by competition and price transparency.
• Single-Payer Viewpoint: The ACA's reliance on private insurers perpetuates administrative complexity and inequity; a universal public system would produce better outcomes at lower cost.
• Full Repeal Viewpoint: The ACA's mandates and regulations are constitutionally dubious and economically harmful; repeal without replacement would restore market function and individual choice.
• Incremental Reform Viewpoint: The law's framework should be preserved but modified - through adjustments to subsidies, market rules, or a public option - to address remaining coverage gaps and cost pressures.

• Affordable Care Act - History
• Affordable Care Act - Debate
• Affordable Care Act - Health Policy Consensus
• Medicaid
• Medicare
• Health Insurance in the United States
• Individual Mandate
• United States of America - History