The Affordable Care Act (ACA), also known as Obamacare, represents one of the most substantial reforms to the U.S. health care system since the establishment of Medicare and Medicaid in the 1960s. The Act was signed into law by President Barack Obama after intense legislative battles occurring over several months and years. It was designed to address the rising cost of health care and to provide health insurance coverage to millions of uninsured Americans. The ACA introduced a variety of measures, including the expansion of Medicaid, the establishment of health insurance exchanges, and mandates requiring individuals to obtain health insurance or face penalties.

The law's provisions aimed to reduce the overall number of uninsured individuals by making insurance more accessible and affordable. Key features of the ACA included protections for people with pre-existing conditions, allowing young adults to stay on their parents' insurance plans until age 26, and providing subsidies for low-income individuals to help them afford coverage through the new health insurance exchanges. The signing of the Act was celebrated by supporters as a historic achievement in American public policy.

However, the ACA faced substantial opposition from many Congressional Republicans and conservative groups who argued that the law represented government overreach and increased health care costs. Despite numerous attempts to repeal the ACA in the years following its passage, it remained a central aspect of U.S. health care policy, giving rise to ongoing debates about health care reform in America.