A population approach and the general right to health and medical care have been important issues in the development of health policy over many centuries. However, equity is still a crucial issue in the planning and evaluation of health care. Many definitions and criteria related to equity have been formulated on the basis of conflicting theories and models. Three dimensions of fair and just resource allocation are essential when needs-based models are used: Equity in access, utilization, and quality of care relative to needs. Health services research should concentrate on such outcome measures regarding equity and the effect of organizational and processual characteristics of health care systems. Prominent examples of such research efforts are presented, but, unfortunately, there are few reliable and systematic data from this kind of study. Health care researchers have a special responsibility towards the population at large to undertake qualified research on equity and to communicate the results to the general public.