Joseph Volotsky — also known as Joseph of Volotsk or Joseph of Volokolamsk (Russian: Ио́сиф Во́лоцкий); secular name Ivan Sanin (Russian: Ива́н Са́нин) (1439 or 1440 – September 9, 1515) — was a prominent Russian theologian and early proponent of , who led the party defending monastic landownership. The Russian Orthodox Church considers him a saint (along with his most notable opponent, Nil Sorsky); his memory is celebrated on 9 September and 18 October (dates in the Julian Calendar).
Joseph Volotsky came from a family of a wealthy landowner (a votchinnik) whose property consisted of the Yazvishche village in the Principaity of Volokolamsk. He learned to read and write at the local monastery and then took the tonsure at the Borovsk Monastery in 1459. Upon the death of its abbot, St. Paphnutius of Borovsk, Joseph Volotsky took his place and attempted to introduce a strict monastic charter. The monks, however, rebuffed his idea, and he had to leave the monastery for good. After having lived in a few other monasteries, Joseph became disappointed with their lax morals and founded his own cloister in 1479 near Volokolamsk, which would become known as the Joseph-Volokolamsk Monastery. Joseph's charter prescribed a monk's chief virtue as absolute obedience to his abbot. All aspects of a monk's life at the monastery were regulated and controlled.
Initially, Joseph Volotsky was connected with the appanage princes of Volokolamsk (brothers of Ivan III) and defended the right of local ecclesiastical and secular feudatories to oppose the authority of the grand prince. Later in his life he severed his relations with the opposition and took the side of the grand prince, sealing this alliance by transferring Joseph-Volokolamsk Monastery to the patronage of Vasili III in 1507.