The historical development of Russian is not easy to trace because until the 17th cent. the religious and cultural language of the Russian people was not Russian, but Church Slavonic. However, within Russia the latter language became sufficiently altered by the vocabulary and pronunciation of spoken Russian to be transformed into a Russian form of Church Slavonic adapted to Russian needs; this change began in early times. The earliest extant document containing Russian elements is an Old Church Slavonic text from the 11th cent. Ukrainian texts can be distinguished from Russian by the late 13th cent., but Belarusian does not definitely appear as a separate language before the 16th cent.
When Peter the Great undertook to Westernize Russia in the early 18th cent., the Russian language was subjected to Western influences and absorbed a number of foreign words. Peter was the first to reform and simplify the Cyrillic alphabet used for Russian. In the late 18th and early 19th cent., partly as a result of the work of the great Russian writer Aleksandr Pushkin, the Russians succeeded in throwing off the dominance of Church Slavonic and in developing their own tongue into a literary language, which was, nevertheless, influenced and even enriched by the Church Slavonic legacy. Literary Russian is based on the dialect used in and around the city of Moscow, which became the leading cultural center of the country in the 15th cent. Extensive reforms, aimed at simplifying and standardizing Russian writing and grammar, took place after the Revolution of 1917.