Reveals the presence of an informal system of valuable support and care for marginalized migrants The United States’ health care system not only consists of a formal safety net, but also an informal and disjointed network of organizations that offer basic care to millions of migrants. This “Third Net” provides free or low-cost health care for the undocumented, low-income, and uninsured migrants who are excluded from the formal system. This groundbreaking study sheds light on the existence of the Third Net and its implications for the overall inequalities in the US health care system. The Third Net is made up of diverse providers with varying levels of service, organizational culture, and mission. These providers operate in unconventional settings, such as mobile clinics on wheels; pop-up clinics in repurposed spaces; and unlicensed, makeshift clinics run by health activists. Despite their unassuming appearances, these clinics are vital resources for marginalized populations that often go unnoticed by the general public, revealing the shortcomings of our formal health care system. By examining these alternative health care spaces, the authors expose the inequities entrenched in the broader health care system and urge a reevaluation of it entirely in order to address these injustices.