Aristocracy (Greek, aristos, “best”; kratos,”power”), form of government in which the sovereign power is vested in a small number of citizens who are theoretically the best qualified to rule, as opposed to monarchy, in which the supreme authority is vested in one person, and to democracy, in which the ultimate authority is exercised by the entire body of citizens or their representatives. In an aristocracy, although the power of government is wielded by a few, theoretically the administration of government is carried on for the welfare of the many. Whenever the interests of the people as a whole are made subservient to the selfish interests of the rulers, aristocracy becomes a form of government known as oligarchy.

Athens, before the period of the Persian wars of the 5th century bc, and Sparta, during practically its entire history, were aristocracies. The same was true of Rome during the period of the Republic, lasting from the 6th to the 1st century bc. Japan during the Heian period (794-1185) was effectively an aristocracy, with a few exalted nobles (mostly from one clan, the Fujiwara) governing on behalf of the puppet emperors. During the European Middle Ages no true aristocracy existed, for although political power reposed in the hands of a few, each feudal lord was sole master in his own domain. In England, the government from the accession of the House of Hanover in 1714 through the 19th century, although parliamentary in form, was in fact an aristocracy, since king and Parliament alike were under the control of a few great Whig families.

At present the term aristocracy is used loosely and in a great variety of combinations to denote a select few with superiority in various categories, for example, an aristocracy of birth, of wealth, or of intellect.