Differences in health across ethnic groups have been documented in the United States and the United Kingdom. The extent to which socioeconomic inequalities underlie such differences remains contested, with many instead focusing on cultural or genetic explanations. In both the United States and the United Kingdom, data limitations have greatly hampered investigations of ethnic inequalities in health. Perhaps foremost of these is the inadequate measurement of ethnicity, but also important is the lack of good data on socioeconomic position, particularly data that address life-course issues. Other elements of social disadvantage, particularly experiences of racism, are also neglected. The author reviews existing evidence and presents new evidence to suggest that social and economic inequalities, underpinned by racism, are fundamental causes of ethnic inequalities in health.