Applications of epidemiologic concepts and methods to health services problems constitute extensions of other successful applications to health and disease problems in populations. Because population medicine is as important as individual medicine for improving and maintaining the health of communities, epidemiology should be regarded as a fundamental science of medicine. Clinical medicine, laboratory medicine, environmental medicine, and population or social medicine should be seen as complementary, not competitive, fields. For administrative medicine and management of health care systems, competence in epidemiology should be regarded as a necessary but not sufficient component of education for this essential branch of medical practice.