Social inequalities in health are extremely high internationally, but they exist also within each country, even in the poorest countries. All stages of life are involved in health inequalities; they are constructed and become established over time, and certain inequalities present during childhood are the harbingers of others in adulthood. The causes of inequalities are multiple, and several levels of explanation coexist, including both proximal causes and fundamental causes. A large number of areas are concerned, including education, access to employment and working conditions, retirement age, housing policy, and lastly policies of redistribution, by taxation and by direct financial aids. Inequalities can be worsened by changes or innovations whose overall effects on health are nevertheless positive. Access to care and the cost of care have direct effects on inequalities. But even if barriers are absent at this level, this is not enough to guarantee equality of care. Social inequities in health both equate to, and result from, social inequities in general.