Never in history has a democracy succeeded in being both diverse and equal, treating different ethnic or religious groups fairly. And yet achieving that goal is now central to the democratic project. It is, Yascha Mounk argues, the greatest experiment of our time. Drawing on history, social psychology, and comparative politics, Mounk explains why we need to create a world in which our ascriptive identities come to matter less not because we ignore global injustices, but because we have succeeded in addressing them.