Teaching the family system concept to physicians is difficult, as it entails a new way of thinking, at odds with the familiar linear medical model that focuses on the individual patient. This conceptual difference and the confusion between working with families in family medicine and family therapy explain the slow or superficial acceptance of family as the unit of care. Five principles have been found to be useful in teaching: (1) specific teaching techniques should take into account previous training and current time constraints; (2) evidence for the relevance of system theory to diagnosis, treatment, and prevention should be evaluated early in the teaching program; (3) clarity of expectations is crucial; (4) emphasis should be on the natural role of the family physician as first-line family advisor and the use of interviewing and observational skills already well developed; and (5) synthesis of the psychosocial and physical aspects of illness will occur naturally if the family physician is the teacher of family system concepts and the role model for their application in practice.