As more is known about the complexity of the relationships between social, economic, and environmental contexts and the health of the population, it appears clear that the concepts of illness and health, while not independent, are not synonymous. A major challenge now facing the field of public health is to organize a true dialogue between the life sciences working mainly on illness seen as a disturbance in one of the functions of a living organism and human sciences dealing with a population's health. Society's challenge is to grant each individual access to high-quality health care services when needed, while developing public policies to promote the health of the population as a whole.