Russian is an
East Slavic language of the wider
Indo-European family. It is a lineal descendant of the language used in
Kievan Rus', a loose conglomerate of
East Slavic tribes from the late 9th to the mid 13th centuries. From the point of view of
spoken language, its closest relatives are
 the other three languages in the East Slavic languages. In many places in eastern and southern
Ukraine and throughout
Belarus, these languages are spoken interchangeably, and in certain areas traditional bilingualism resulted in language mixtures such as
Surzhyk in eastern Ukraine and
Belarus. An East Slavic
Old Novgorod dialect, although vanished during the 15th or 16th century, is sometimes considered to have played a significant role in the formation of modern Russian. Also Russian has notable lexical similarities with Bulgarian due to a common
Church Slavonic influence on both languages, as well as because of later interaction in the 19th and 20th centuries, although Bulgarian grammar differs markedly from Russian. In the 19th century, the language was often called "
Great Russian" to distinguish it from Belarusian, then called "White Russian" and Ukrainian, then called "Little Russian".
vocabulary (mainly abstract and literary words), principles of word formations, and, to some extent, inflections and literary style of Russian have been also influenced by
Church Slavonic, a developed and partly russified form of the
Old Church Slavonic language used by the
Russian Orthodox Church. However, the East Slavic forms have tended to be used exclusively in the various dialects that are experiencing a rapid decline. In some cases, both the East Slavic and the
Church Slavonic forms are in use, with many different meanings. For details, see
Russian phonology and
History of the Russian language.
Over the course of centuries, the vocabulary and literary style of Russian have also been influenced by Western and Central European languages such as
 and to a lesser extent the languages to the south and the east:
Arabic, as well as
According to the
Defense Language Institute in
Monterey, California, Russian is classified as a level III language in terms of learning difficulty for native
English speakers, requiring approximately 1,100 hours of immersion instruction to achieve intermediate fluency.
 It is also regarded by the
as a "hard target" language, due to both its difficulty to master for English speakers and its critical role in
American world policy.