KIE: The meaning of health, its relation to illness and disease, and its aspects that are of particular importance in medical ethics are the foci of Gillon's essay, one of a series on philosophical medical ethics. He argues that the World Health Organization's definition of health--"a state of complete physical, mental, and social wellbeing and not merely the absence of disease or infirmity"--is too broad for use by physicians in patient care. Defining illness and disease--those components of ill health with which doctors are concerned--might help delineate the physician's role in restoring or preserving health. Gillon summarizes the realist and nominalist approaches to disease and to the question whether it is an evaluative or a value free concept. He suggests that the definition and ascription of illness are of such social importance that decisions concerning them should be made cooperatively by doctors and society.