Absolutism is a political system in which a single sovereign ruler or leader holds complete and unrestrained power over a country. It is a form of monarchical power that is unrestrained by all other institutions, such as churches, legislatures, or social elites). The essence of an absolutist system is that the ruling power is not subject to regularized challenge or check by any other agency, be it judicial, legislative, religious, economic, or electoral. Absolutism is typically used in conjunction with some European monarchs during the transition from feudalism to capitalism, and monarchs described as absolute can especially be found in the 16th century through the 19th century).

The most commonly studied form of absolutism is absolute monarchy, which originated in early modern Europe and was based on the strong individual leaders of the new nation-states that were created at the breakup of the medieval order. The power of these states was closely associated with the power of their rulers; to strengthen both, it was necessary to curtail the restraints on centralized government that had been exercised by the church, feudal lords, and medieval customary law. By claiming the absolute authority of the state against such former restraints, the monarch as head of state claimed his own absolute authority.

Absolutism has existed in various forms in all parts of the world, including in Nazi Germany under Adolf Hitler and in the Soviet Union under Joseph Stalin.