Eastern Orthodox Church
Present
The main traditional historical communion is divided into two groups—those who use the Revised Julian calendar for calculating fixed feasts and the Julian calendar for calculating movable feasts, and those who use the Julian calendar for all purposes. This second group may include congregations whose church allows them to choose, with the proviso that the choice remains in effect at least until the end of the church year. Also in communion are the Estonian and Finnish Orthodox churches who have a dispensation to use the Gregorian calendar for all purposes. Another group is referred to as True Orthodoxy (or Old Calendarists); they are those who, without authority from their parent churches, have continued to use the old Julian calendar, claiming that the calendar reform in the 1920s is in contravention of the ecumenical councils. Similarly, another group called the Old Believers, separated in 1666 from the official Russian Orthodox Church as a protest against church rite reforms introduced by Patriarch Nikon of Moscow. As Eastern Orthodox Christianity is both collegial and local in structure, there is no single organization called the "True Orthodox Church" nor is there official recognition among the "True Orthodox" as to who is properly included among them. While some unions have taken place even up to the present, the majority of True Orthodox are only secondarily concerned with reunion as opposed to preservation of Eastern Orthodox teaching.
Eastern Orthodox Church-207