As we consider how to improve health care, we must understand the transformation that focuses on the physician's role in health care. A multidisciplinary team is critical for improvement activities-hospital administrators, nurses, and other colleagues. All need to learn new knowledge and leadership skills, but there is a special need to understand underlying issues that will require a transformation in many physicians. This will not be easy-nor should it be. Physicians must continue to achieve the benefits for patients that come from traditional professional knowledge. However, there is an even greater need to understand how physicians can move from the dominance approach of the medical model to a partnership approach inherent in CQI. This article describes lessons learned from our CQI work with physician colleagues over the last several years. First the relationship of professional knowledge to knowledge for improvement is described, and then the individual patient-doctor relationship is reexamined. Next, the implications of knowledge for improvement for the roles of physicians in organized health care systems are considered.