It seems that we all have a moral obligation to restore, preserve and enhance health, our own and that of others, e.g. that of our children or parents. It is also an imperative within health care, medicine and public health, to support and enhance people’s health. Health is, furthermore, thought to be a human right. In its most ambitious formulation health is not only "a fundamental human right”, but “the attainment of the highest possible level of health” is “a most important worldwide social goal” (WHO 1986). These ethical imperatives make it important to discuss what health is, and what kinds of enhancement are increases in health and what kinds are not. This paper presents different attempts to draw a demarcation line between processes and states that we believe should belong to the concept of health, and processes and states which we believe should not belong to it. Since all we can expect to produce is a nominal definition, some initial criteria for the explication of health are presented. On the basis of these criteria, a holistic, pluralistic theory is suggested. The theory defines health in terms of basic abilities and well-being. A distinction is also made between manifest health, i.e. the ability and well-being here and now, and basic or fundamental health, i.e. the internal foundations for manifest health. Given these conceptual starting points, the remainder of the paper discusses various ways of trying to differentiate between enhancement that is an increase in (the various aspects of) health, and enhancement that is not, e.g. if there is a distinction between reducing ill health, and promoting positive health, or between “normal” and “supernormal” enhancement. It also discusses if the means used matter, e.g. if wheel-chairs, implants, medicine, narcotics, or genetic manipulation enhance health, if they only compensate for the lack of it, or if they enhance something else, such as non-health-related abilities, capacities or competences. Finally, the paper makes some suggestions towards distinguishing substances that are health-enhancing and those that are non-health-enhancing, e.g. those that are normal to humans, or normal in the culture, those which individuals need in order to live and to flourish, and those that can be tolerated in the long run by the human body and mind.