In this article, I try to show how the principle of fair play provides insight into the problem of excessive incarceration. I also address the concern that democratic societies are especially susceptible to this problem because of their tendency to foster what has come to be called penal populism. My argument is that democracy leads to mass imprisonment only when an otherwise democratic polity neglects what Albert Dzur calls the “moral dimension” of government by the people. In particular, this moral dimension requires an understanding of the polity as a cooperative enterprise according to rules that specify the terms of fair play. Mass incarceration of the kind that now characterizes the United States is a sign that this polity is failing to play fair when it imprisons many of those who violate its laws.