Illuminati (Lat., the enlightened), a name supposed to have been given to the newly baptized in the early Christian church, because a lighted taper was put into their hands as a symbol of enlightenment; subsequently a name assumed at different periods by sects of mystics or enthusiasts who claimed a greater degree of illumination or perfection than other men. The most famous of these sects were the Alombrados or Alumbrados (the enlightened) in Spain at the end of the 16th century; the Guerinets, named after their founder Pierre Guerin, in France in the 17th century; and an association of mystics in Belgium in the 18th. The most celebrated society of the name was that founded in 1776 by Adam Weishaupt, a German professor of canon law at Ingolstadt, and a man of great originality and depth of thought, with the ostensible object of perfecting human nature, of binding in one brotherhood men of all countries, ranks, and religions, and of surrounding the persons of princes with trustworthy advisers. Apostles, styled areopagites, were sent to various parts of Europe to make converts, and before the existence of the society became generally known branches had been established in various parts of Germany, in Holland, and in Milan. Young men from 18 to 30 years of age, and Lutherans rather than Roman Catholics, were preferred as members.

The illuminati gained much influence by the accession to their ranks of Knigge the author, and by the sympathy of many freemasons. At the height of its prosperity the society had 2,000 members. The order was divided into three classes and several subdivisions. The first, or preparatory class, was divided into novices, minervals, and illuminati minores. The second class was that of the freemasons, who were ranked as apprentices, assistants, and masters; it included two higher grades, that of the illuminatus major, or of the Scottish novice, and that of the illuminatus dirigens, also called the Scottish knight. The class of mysteries was divided into major and minor mysteries, of which the latter included the two grades of priests and regents. The major mysteries comprised the grades of magus and rex. The mysteries related to religion, which was transformed into naturalism and free thought, and to politics, which inclined to socialism and republicanism. The order corresponded in cipher, and used a peculiar phraseology; January was called Dimeh; February, Beumeh; Germany, the Orient; Bavaria, Achaya; and Munich, Athens. Every illuminatus received a new name; Weishaupt was Spartacus, and Knigge was Philo. But Knigge and Weishaupt could not agree, and this, as well as the opposition of the Roman Catholic clergy, proved fatal.

The society was prohibited by the Bavarian government in 1784, and its papers were seized and published under the title Ei-nige Originalschrif'ten des Illuminatenordens, auf hochsten Befehl gedruckt (Munich, 1787). Works on the subject were published by Weishaupt, Knigge, Nicolai, and Voss (1786-'99).