Along the arduous, confusing, and contentious road to the enactment and implementation of the Affordable Care Act (ACA), no single date stands out as more consequential for the health and well-being of the US public as does January 1, 2014. Barring unforeseen circumstances, this date will stand out as transformational in the annals of US health care reform. On that day, 4 fundamental provisions of the ACA will take effect. First, extension of the “guaranteed issue” provision to all individual health insurance policies inclusive of the elimination of “medical underwriting” in the face of a preexisting condition. Second, implementation of the “individual shared responsibility” provision also known as the “individual mandate.” Third, provision of tax credits and cost-sharing subsidies to middle- and lower-income adults for the purchase of individual health insurance. And fourth, expansion of Medicaid coverage in participating states to include previously ineligible low-income adults. Most Americans, including physicians and other health care professionals, may not appreciate the profound nature of these new realities. This oversight could be attributable to the daily dramas and controversies of the government shutdown, the woes of the HealthCare.gov website, the cancelation of individual health insurance policies, and the establishment of limited physician networks. In this Viewpoint, we assess the significance of the reforms in question and the implications thereof for the US health care system.