Old Church Slavonic (, ), also known as
Old Church Slavic (; often abbreviated to
OCS; self-name ,
slovenisku jezyku), was the first
Slavic literary language. The 9th-century
Byzantine missionaries
Saints Cyril and Methodius of
Slavic,
Greek descent, or both, are credited with
standardizing the language and using it in translating the
Bible and other
Ancient Greek ecclesiastical texts as part of the
Christianisation of the
Slavic peoples. It is thought to have been based primarily on the dialect of the 9th century
Byzantine Slavs living in the
Province of Thessalonica (now in
Greece). It played an important role in the history of the Slavic languages and served as a basis and model for later
Church Slavonic traditions, and some
Eastern Orthodox and
Eastern Catholic churches use this later Church Slavonic as a
liturgical language to this day. As the oldest attested Slavic language, OCS provides important evidence for the features of
Proto-Slavic, the reconstructed common ancestor of all Slavic languages.