Health insurance, poverty, and health are all interconnected in the United States. This article synthesizes a large and compelling body of health services research, finding a strong association between health insurance coverage and access to primary and preventive care, the treatment of acute and traumatic conditions, and the medical management of chronic illness. Moreover, by improving access to care, health insurance coverage is also fundamentally important to better health care and health outcomes. Research connects being uninsured with adverse health outcomes, including declines in health and function, preventable health problems, severe disease at the time of diagnosis, and premature mortality.