An international groundswell of activity is seeking to identify and reduce the use of health care services that provide little or no benefit—whether through overuse or misuse. There are strong imperatives for identifying such waste: (1) an ethical imperative to ensure patient safety and thus avoid tests and treatments that cause harm directly or indirectly without providing commensurate benefit; (2) a quality imperative to measure and reward best practices; and (3) an economic imperative to reduce spending and enhance the diffusion of cost-effective innovations.