Patriarch Nikon of Moscow ordered the Russian church's liturgical books and ritual gestures corrected to match contemporary Greek practice in 1652, replacing the two finger sign of the cross with three fingers, altering the spelling of Jesus's name, and revising chant and prostration rules that had stood since the Christianization of Rus. A Great Council in 1666 to 1667 endorsed the reforms and anathematized everyone who kept the older forms, and those who refused, the Old Believers, were declared schismatic and hunted as such for the better part of two centuries under both church and state authority.
Persecution shaped what the movement became more than doctrine did. Communities fled into remote forests and the far north to keep the old rite, some burning themselves alive rather than accept the new books, a practice remembered as the self immolations. Because bishops stayed loyal to the reformed church almost without exception, the Old Believers lost the ability to ordain new priests from within their own ranks, and the movement split on how to survive that loss.
The priested Old Believers, Popovtsy, kept sacramental life going by receiving clergy who defected from the official church, eventually securing their own bishop in 1846 and building a parallel hierarchy that still ordains today. The priestless, Bezpopovtsy, concluded no legitimate priesthood remained at all after Nikon, and built communities such as the Vyg settlement around lay leadership, with baptism and confession retained but the eucharist itself set aside as something only a valid priest could offer, a decision some priestless groups have never reversed.