Abstract: Inequalities in health arise from inequalities in society. Small differences in society result in small health inequalities; large differences result in large health inequalities.1 Differences in access to health care matter, as do differences in lifestyle, but the key determinants of social inequalities in health lie in the circumstances in which people are born, grow, live, work, and age. These, in turn, arise from differential access to power and resources. Such was the conclusion of the World Health Organization Commission on Social Determinants of Health (CSDH).2 The CSDH had an optimistic tone. Reviewing evidence from around the world, and reaching judgements on what works, it concluded that it is indeed possible to make great progress in closing health gaps — in a generation.