This article reviews 98 studies examining the association between income inequality and health, both at the aggregate and multilevel levels. The review finds limited support for the idea that income inequality is a major determinant of population health differences within or between rich countries. While income inequality may directly influence some health outcomes, such as homicide in certain contexts, the strongest evidence for direct health effects is among U.S. states, though even this is somewhat mixed. Despite the lack of strong evidence for a direct effect of income inequality on health, reducing income inequality by improving the incomes of the most disadvantaged can improve their health, reduce health inequalities, and generally enhance population health. The article discusses various theoretical frameworks that have been proposed to understand the relationship between income inequality and health, including the psychosocial and neomaterial interpretations. It also reviews the evidence from international and within-country studies, finding that while some studies support the income inequality hypothesis, others show no or mixed associations. The review concludes that the direct health effects of income inequality are generally modest, but they can have a significant impact on a large segment of the population.This article reviews 98 studies examining the association between income inequality and health, both at the aggregate and multilevel levels. The review finds limited support for the idea that income inequality is a major determinant of population health differences within or between rich countries. While income inequality may directly influence some health outcomes, such as homicide in certain contexts, the strongest evidence for direct health effects is among U.S. states, though even this is somewhat mixed. Despite the lack of strong evidence for a direct effect of income inequality on health, reducing income inequality by improving the incomes of the most disadvantaged can improve their health, reduce health inequalities, and generally enhance population health. The article discusses various theoretical frameworks that have been proposed to understand the relationship between income inequality and health, including the psychosocial and neomaterial interpretations. It also reviews the evidence from international and within-country studies, finding that while some studies support the income inequality hypothesis, others show no or mixed associations. The review concludes that the direct health effects of income inequality are generally modest, but they can have a significant impact on a large segment of the population.