As much as we have struggled for equality, we have always been profoundly skeptical about it. How much do we want, and for whom? This book is the definitive intellectual history, tracing equality’s global origins and spread from the dawn of humanity through the Enlightenment to today. Equality has been reimagined continually, in the great world religions and the politics of the ancient world, by revolutionaries and socialists, Nazis and fascists, and postwar reformers and activists. A magisterial exploration of why equality matters and why we continue to reimagine it, this book offers all the tools to rethink equality anew for our own age.