Old calendarists

Old calendarists may refer to any of the following:

Those Eastern Orthodox churches (e.g., the Greek Old Calendarists) who suspended full communion and/or concelebration with the mainstream churches over the adoption by the latter of the Revised Julian calendar ("New calendarists"). This is the most common use of the term.
Those Eastern Orthodox churches which remain in full communion with the New calendarists and yet continue to use the Julian calendar, including the Orthodox Church of Jerusalem, Russian Orthodox Church, Serbian Orthodox Church, and the Georgian Orthodox Church. (The Julian calendar is also used by the Russian Orthodox Church Outside of Russia which is in the process of reunion with the Russian Orthodox Church.)