At the end of III– beginning of II Millennium BC from the Indo-European family separated the proto-Slavic language which is the basis for Slavic languages. In X – XI century Slavic language was divided into 3 groups of languages: West Slavic (from it there was Polish, Czech, Slovak), South Slavic (developed in the Bulgarian, Macedonian, Serbo-Croatian) and Eastern Slavic.
In the period of feudal fragmentation, which contributed to the formation of regional dialects, and the Mongol-Tatar yoke of the East Slavic has developed three separate languages: Russian, Ukrainian, Belarusian. Thus, the Russian language belongs to the East Slavic (old Russian) subgroup of the Slavonic group of the Indo-European language branch.