The Institute for Clinical Systems Integration (ICSI) is a non-profit quality improvement organization that bridges 20 medical groups and integrated health care systems in the Minneapolis-St. Paul area. Created in 1992 by HealthPartners, HealthSystem Minnesota, and Mayo Clinic as a part of a contract awarded by the Buyers Health Care Action Group, a purchaser coalition, ICSI's aim is collaborative, continual improvement of the clinical care provided by its member institutions. ICSI's main focus is health care guideline developement and implementation. This article describes this process, as well as evidence of program effectiveness and "lessons learned."