Old Calendarists are groups of Orthodox Christians who are in various levels of "resistance" against the mainstream Orthodox churches, identified mainly by their insistence on the use of the Julian Calendar. They are to be distinguished from the mainstream churches which simply follow the Julian Calendar yet remain in full communion with most or all of world Orthodoxy. Many Old Calendarists today say that their concerns about ecumenism are more significant than calendar issues.
The mainstream churches have varying positions on different Old Calendarist churches, ranging from an active desire to restore unity to a denial of the Old Calendarists' Orthodoxy.
Some Old Calendarist groups are styled as True Orthodox or Genuine Orthodox, and both terms are used in this article.
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