The gap between the haves and the have-nots has alternately grown and shrunk throughout the course of human civilization. Economic inequality may only recently have returned to great prominence in popular discourse, but its history runs deep. My book seeks to track and explain this history in the very long run. One of the first to draw my attention to this very long run was Branko Milanovic, a world expert on inequality who in his own research has reached all the way back to antiquity. If there were more economists like him, more historians would be listening. About a decade ago, Steve Friesen made me think harder about ancient income distributions, and Emmanuel Saez further piqued my interest in inequality during a shared year at Stanford’s Center for Advanced Study in the Behavioral Sciences.