Recent disputes over whether older people should pay more for health insurance, or receive lower priority for transplantable organs, highlight broader disagreements regarding the legality of using age-based criteria in health care. These debates will likely intensify given the changing age structure of the American population and the turmoil surrounding the financing of American health care. This Article provides a comprehensive examination of the legality and normative desirability of age-based criteria. I defend a distributive justice approach to age-based criteria and contrast it with two prevailing theoretical approaches to age-based criteria, nondiscrimination and discretion. I propose a detailed normative framework for the use of age-...