There are dramatic differences in health between countries and within countries. But this is not a simple matter of rich and poor. A poor man in Glasgow is rich compared to the average Indian, but the Glaswegian’s life expectancy is 8 years shorter. In all countries, people at relative social disadvantage suffer health disadvantage, and dramatically so. Within countries, the higher the social status of individuals, the better is their health. But globally these health inequalities defy usual explanations. Creating the conditions for people to lead flourishing lives, and thus empowering individuals and communities, is key to development. Datar reports for BBC World News.