A growing body of research confirms the existence of a powerful connection between socioeconomic status and health. This research has implications for both clinical practice and public policy and deserves to be more widely understood by physicians. Absolute poverty, which implies a lack of resources deemed necessary for survival, is self-evidently associated with poor health, particularly in less developed countries. Over the past two decades, economic decline or stagnation has reduced the incomes of 1.6 billion people. Strong evidence now indicates that relative poverty, which is defined in relation to the average resources available in a society, is also a major determinant of health in industrialized countries. For example, persons in U.S. states with income distributions that are more equitable have longer life expectancies than persons in less egalitarian states. There are numerous possible approaches to improving the health of poor populations. The most essential task is to ensure the satisfaction of basic human needs: shelter, clean air, safe drinking water, and adequate nutrition. Other approaches include reducing barriers to the adoption of healthier modes of living and improving access to appropriate and effective health and social services. Physicians as clinicians, educators, research scientists, and advocates for policy change can contribute to all of these approaches. Physicians and other health professionals should understand poverty and its effects on health and should endeavor to influence policymakers nationally and internationally to reduce the burden of ill health that is a consequence of poverty.