Health systems in developing countries face enormous problems. In all of the poorest countries—and even in most rich ones—health outcomes vary widely by socioeconomic group. Governments and insurance companies alike are struggling to meet the costs of ever-increasing public expectations for health services. In many countries, households in which a family member suffers from a chronic disease are driven into (or kept in) poverty by the catastrophic cost of ongoing medical care. At the same time, vast sums are being wasted on ineffective—or even harmful—interventions, and enormous technical inefficiencies plague the delivery of health services.