Expanding upon the concept of totalitarianism, this study introduces the concept of ideocracy to encompass all those political systems that legitimize their actions by reference to an all-inclusive utopian ideology. It distinguishes pluralist systems, marked by competing schools of thought, from monistic systems in which a utopian ideology is dominant. Focusing on twentieth-century regimes, the authors develop Weberian ideal-type models to clarify different forms of ideocracy and pluralism; explore the ideal-type model of ideocracy; and analyze the dynamics of political life using models that...