If we compare health and wellbeing in different countries, it’s clear that some societies do much better than others. And the countries that do well on one measure, life expectancy for example, tend to do well across the board – with better health, better educational outcomes, better community wellbeing, and so on. Countries that do badly on one, also tend to do badly across the board. So what’s going on? Surprisingly, it isn’t how rich a society is that matters; it’s how unequal it is that really counts. Inequality has always been regarded as divisive and socially corrosive, and now the evidence supports that intuition. This talk, at Humanists UK Convention 2023, explores the extent to which the question of inequality is central to meeting the grand challenge of creating sustainable wellbeing for everyone.