'''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 [[Old 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.