Patient navigation is a patient-centric health care service delivery intervention, the principal purpose of which is to eliminate barriers, which may occur across the health care continuum, to timely diagnosis and treatment of cancer and other chronic diseases. This intervention, which was pioneered in Harlem, NY, is being widely replicated nationally and is receiving considerable support for demonstration projects and research to test its effectiveness. This article reviews the history of the development of patient navigation and outlines the basic principles of this intervention based on two decades of experience.