Ancien Régime means Old Rule or Old Order in French; in English, the term refers primarily to the social and political system established in France under the Valois and Bourbon dynasties. More generally it means any regime which shares the former's defining features: a feudal system under the control of a powerful absolute monarchy supported by the doctrine of the Divine Right of Kings and the explicit consent of the established Church, essentially how Europe had been organized since at least the 8th century.

The term is from The Age of Enlightenment (first appearing in print in English 1794) and was originally pejorative in nature. Similar to other sweeping criticisms of the past, such as the term Dark Ages, the concept of Ancien Régime is layered onto the past as an expression of disapproval for the way things were done, and carries an implied approval of a "New Order". No one alive during the Ancien Régime saw themselves as living under an "Old Order". The term was created by Enlightenment era authors to promote a new cause and discredit the existing order, and thus was not, in its origin, a neutral historical descriptor of the past.

As defined by the creators of the term, the Ancien Régime developed out of the French monarchy of the Middle Ages, and was swept away centuries later by the French Revolution of 1789. Europe's other ancien régimes had similar origins, but diverse ends: some gradually became constitutional monarchies, others were torn down by wars and revolutions.

The analogous term "Antiguo Régimen" is often used in Spanish. However, although Spain was strongly affected by the French Revolution and its aftermath, the break was not as sharp as in France.

Power in the Ancien Régime relied on three pillars: the monarchy, the clergy, and the aristocracy. Society was divided into three Estates of the realm: the First Estate, the Roman Catholic clergy; the Second Estate, the nobility; and the Third Estate, the rest of the population.

See also: Old Europe, France under the Ancien Régime