Fedoseevtsy, also Fedoseyans (федосеевцы, феодосиевцы in Russian), sometimes anglicised as Theodosians, comprise a dissident religious movement formed in Imperial Russia.
The Fedoseevtsy movement, founded by an ex-deacon Feodosy Vasilyev [ru] (1661-1711), originated amidst Old Believers (mostly peasants and posad people) in Northwest Russia.
The Fedoseevtsy disapproved of a certain group within the Bespopovtsy, namely the Pomortsy, who had been diverging from the strict principles of the Old Believers and had adopted the custom of praying for the Tsar (моление за царя).
In the late-18th century, the Fedoseevtsy centered on a group led by Ilya Kovylin [ru] (1731-1809) with their all-Russian "headquarters" at the Preobrazhenskoye cemetery in Moscow.
In the second half of the 19th century, a group of the so-called "newlyweds" (новожёны) detached itself from the Fedoseevtsy movement, acknowledging the institution of marriage.