Health and disease are cardinal concepts of the biomedical sciences and technologies. Though the models of health and disease may vary, these concepts play a defining role, indicating what should and what should not be the objects of medical concern. The concepts are ambiguous, operating both as explanatory and evaluatory notions. They describe states of affairs, factual conditions, while at the same time judging them to be good or bad. Health and disease are normative as well as descriptive. This dual role is core to their ambiguity and is the focus of this paper. In this paper I shall examine first the concept of health; second, the concept of disease; and third, I will draw some general conclusions concerning the interplay of evaluation and explanation in the concepts of health and disease.