Most quality improvement projects address care delivered in one service of a hospital, such as the operating suite or the obstetrics service. Some projects are collaborative efforts involving groups of hospitals with similar interests. Few projects attempt to change care on a population basis (i.e., involving all providers in entire states or the nation as a whole.) The Cooperative Cardiovascular Project (CCP), sponsored by the Health Care Financing Administration, is attempting to improve care for all Medicare patients suffering from acute myocardial infarctions nation-wide. The CCP has been active since 1993 and, in a pilot project, has demonstrated that care can be improved on a population basis (i.e., in four entire states). This article explores the lessons learned from the CCP pilot and from the evolving CCP national experience.