Together with Ukrainian and Belarusian, the Russian language makes up the eastern branch of the Slavic family of languages. Russian is the primary language of the overwhelming majority of people in Russia and is also used as a second language in other former republics of the Soviet Union. Russian was also taught extensively in those countries lying within the Soviet sphere of influence, especially in eastern Europe, in the second half of the 20th century. Russian dialects are divided into the Northern group (stretching from St. Petersburg eastward across Siberia), the Southern group (in most of central and southern Russia), and the Central group (between Northern and Southern). Modern literary Russian is based on the Central dialect of Moscow, having basically the consonant system of the Northern dialect and the vowel system of the Southern dialect. The differences between these three dialects are fewer than between the dialects of most other European languages, however.

Russian and the other East Slavic languages (Ukrainian, Belarusian) did not diverge noticeably from one another until the Middle Russian period (the late 13th to the 16th century). The term Old Russian is generally applied to the common East Slavic language in use before that time.