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 allow readers to examine the contradictions and evolutionary paths of specific political systems. In addition, they examine diverse psychological, social, and environmental factors in analyzing the emergence of ideocracies and their subsequent evolution and emphasize that although these systems may persist for extended periods, they may also evolve into other forms of government through processes ranging from radical transformation to gradual erosion.