Federal health officials are now encouraging health systems to be innovative in developing cost-efficient ways to treat Medicare patients. One of the government's latest tools is "the accountable care organization," or ACO—a network of providers that manages the health of a specific population of Medicare patients. There are built-in financial inducements to keep the patients well, not just to treat them when they are sick. Providers share with the government in any cost savings from managing a healthier population. The St. Louis area's leading health systems are experimenting with ACOs and related models of coordinated care.