Never in history has a democracy succeeded in being both diverse and equal, treating members of many different ethnic or religious groups fairly. And yet achieving that goal is now central to the democratic project in countries around the world. Drawing on history, social psychology, and comparative politics, Yascha Mounk examines how diverse societies have long suffered from the ills of domination, fragmentation, or structured anarchy. To make diverse democracies endure, and even thrive, we need to create a world in which our ascriptive identities come to matter less—not because we ignore the injustices that still characterize the United States and so many other countries around the world, but because we have succeeded in addressing them. The Great Experiment is that rare book that offers both a profound understanding of an urgent problem, and genuine hope for our human capacity to solve it.