By 2050 an estimated 83.7 million Americans will be ages sixty-five and older, up from 40.3 million in 2010. The shock wave of aging Americans will have profound implications for older people, their families, health care providers, and the economy. Researchers, policy makers, health care leaders, and others are designing responses to the challenges these actuarial shifts will create. For example, delivering health care at home could help keep more older Americans out of costly emergency departments and nursing homes. But such steps require more health care providers, a broader distribution of providers than currently exists, and better use of the resources we have.