Decanonization or de-canonization (prefix de- ← Latin: de  preposition: down, from, away^[1][2] + Latin: canonizatio ← Greek: κανών – list, catalog^{[3][4][5][6][7]}) – exclusion of a person's name from the list, catalog; the opposite of canonization. The list or catalog is the calendar of the saints^[8][9] or the church calendar. Decanonization, the exclusion of the saint's name from the calendars, was carried out in the Russian Orthodox Church,^[10][11] in the Catholic Church^{[12][13][14][15]} and in the Anglican Church.^[16][17]

In the Russian Orthodox Church, the most famous case is the decanonization of the Right-Believing princess of Anna of Kashin at the Great Moscow Synod in 1677–1678. The reason for the decanonization was the religious policy of the forcible introduction in Russia of the three fingers sign of the cross, instead of the older two fingers variant.^[18][19] The reforms that began under Alexis Mikhailovich and continued under Peter I and his followers demanded a political and ecclesiastical separation from the previous tradition and national culture. First of all, decanonization affected persons whose literary works or hagiographic works contradicted the new religious policy. The veneration of the famous ecclesiastical writer and translator, the Maximus the Greek, was suspended. Memorial days associated with 21 Russian saints have disappeared from the Typikon of 1682.^[20] In Peter's times, the veneration of the martyrs Anthony, John, and Eustathius, who wore beards, suffered from a clean-shaven pagan knyaz, was stopped.^[21] After 1721 the number of canonizations sharply decreased (only 2) and decanonizations began (there were, of course, much more than 8 of them). In the XVIII century there was a decanonization of a number of locally revered saints, and in the 19th century church veneration of many locally venerated saints was restored. Hegumen Andronik (Trubachev) believes that the most pernicious were not specific decanonizations, but the very admission of decanonization into church life as a possible norm, a rule implemented due to a change in church policy.^[22]

In the 20th century, some of the names of previously decanonized saints were returned to the church calendar. The re-canonization of Anna Kashinskaya took place in the Russian Church in 1909. However, most of the ancient Russian ascetics, whose veneration was terminated during the "struggle against Raskol", remained forgotten.^[23]

In 2013, 36 saints, New Martyrs who suffered from repression during the Soviet era, were decanonized. Their names were removed from the 2013 Russian Orthodox Church calendar without explanation.^{[24][25][26][27][28]}

There is a group of people who consider the term "decanonization" to be incorrect, as a rule these are persons affiliated with religious structures. They believe that the saints still remain in Heaven. They reject the very possibility of decanonization. They regard canonization as an infallible act that cannot be corrected.^{[29][30][31][32][33]}