It seems more than coincidental that at a time of great concern over rising health care costs and fears of rampant technology, debates are suddenly taking place about medical futility and health care rationing. This article examines the economic, historical, and demographic factors that have motivated increased attention to both these concepts, explores differences and similarities in the meaning of these terms, and discusses their ethical implications. Specifically, we identify four common sources of current debates on futility and rationing: the rise in health care costs; the development of high-technology medicine; the aging of society; and the effort to limit the scope of patient autonomy. We propose that when rationing criteria refer to medical benefit, the meanings of futility and rationing share certain common features. Futility and rationing differ, however, in important ways. Futility refers to treatment and outcome relationships not in a general population but in a specific patient. Rationing criteria usually are supported by reference to theories of justice, whereas the definition of futility, if achieved, will probably be arrived at by empirical community agreement. Rationing always occurs against a backdrop of resource scarcity, but futility need not. Toward the end of the paper, we clarify how the various connotations and contexts we associate with each term enhance or frustrate ethical debate.