Ecclesia Gnostica Catholica

Ecclesia Gnostica Catholica (E.G.C.), or the Gnostic Catholic Church, is the ecclesiastical arm of Ordo Templi Orientis (O.T.O.), an international fraternal initiatory organization devoted to promulgating the Law of Thelema. Thelema is a philosophical, mystical and religious system elaborated by Aleister Crowley, and based on The Book of the Law. The word Catholic denotes the universality of doctrine and not a Christian or Roman Catholic belief set.

The chief function of Ecclesia Gnostica Catholica is the public and private performance of the Gnostic Mass (Liber XV), a eucharistic ritual written by Crowley in 1913. According to William Bernard Crow, Crowley wrote the Gnostic Mass "under the influence of the Liturgy of St. Basil of the Russian Church." Its structure is also influenced by the initiatory rituals of the Ordo Templi Orientis. Its most notable separation from similar rites of other churches is a Priestess officiating with a Priest, Deacon, and two Children. In addition to the Eucharist, baptism, confirmation, marriage, and last rites are offered by E.G.C. Marriage is not limited to couples of opposite gender.

About the Gnostic Mass, Crowley wrote in The Confessions of Aleister Crowley, "... the Ritual of the Gnostic Catholic Church ... I prepared for the use of the O.T.O., the central ceremony of its public and private celebration, corresponding to the Mass of the Roman Catholic Church." It is the single most commonly performed ritual at O.T.O. bodies, with many locations celebrating the Mass monthly or more frequently. Most O.T.O. bodies make some or all of these celebrations open to interested members of the public, so the Mass is often an individual's first experience of the O.T.O.

Ecclesia Gnostica Catholica has a hierarchical structure of clergy, assisting officers, and laity which parallels the degree structure of the O.T.O. initiatory system. Before 1997, the two systems were more loosely correlated, but since then there have been strict rules concerning minimum O.T.O. degrees required to serve in particular E.G.C. roles.