In 1984, the 32 member states of the World Health Organization European Region took a remarkable step forward in agreeing unanimously on 38 targets for a common health policy for the Region. Not only was equity the subject of the first of these targets, but it was also seen as a fundamental theme running right through the policy as a whole. However, equity can mean different things to different people. This article looks at the concepts and principles of equity as understood in the context of the World Health Organization's Health for All policy. After considering the possible causes of the differences in health observed in populations--some of them inevitable and some unnecessary and unfair--the author discusses equity in relation to health care, concentrating on issues of access to care, utilization, and quality. Lastly, seven principles for action are outlined, stemming from these concepts, to be borne in mind when designing or implementing policies, so that greater equity in health and health care can be promoted.