For decades, health professionals have asserted the importance of public participation in interventions for health. Medicine has pursued patient participation in clinical decision-making. In the public health realm, target groups have been asked to assist in the design and implementation of initiatives for health. In practice, however, patients and populations expect health professionals to give advice and - in some cases - to make decisions on their behalf. This implies limits to the ideal of participation. In this innovative work, the author contrasts public and professional understandings of health and the best ways to achieve health. The result is a model of lay participation in the