However, the East Slavic forms have tended to remain 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 slightly different meanings. For details, see Russian phonology and History of the Russian language.

Russian phonology and syntax (especially in northern dialects) have also been influenced to some extent by the numerous Finnic languages of the Finno-Ugric subfamily: Merya, Moksha, Muromian, the language of the Meshchera, Veps etc. These languages, some of them now extinct, used to be spoken right in the center and in the north of what is now the European part of Russia. They came in contact with Eastern Slavic as far back as the early Middle Ages and eventually served as substratum for the modern Russian language. The Russian dialects spoken north, north-east and north-west of Moscow have a considerable number of words of Finno-Ugric origin. The vocabulary and literary style of Russian have also been greatly influenced by Greek, Latin, French, German, and English. Modern Russian also has a considerable number of words adopted from Bulgarian, Tatar and some other Turkic languages.

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 780 hours of immersion instruction to achieve intermediate fluency. It is also regarded by the United States Intelligence Community as a "hard target" language, due to both its difficulty to master for English speakers as well as due to its critical role in American foreign policy.

Geographic distributionRussian is primarily spoken in Russia and, to a lesser extent, the other countries that were once constituent republics of the USSR. Until 1917, it was the sole official language of the Russian Empire. During the Soviet period, the policy toward the languages of the various other ethnic groups fluctuated in practice. Though each of the constituent republics had its own official language, the unifying role and superior status was reserved for Russian. Following the break-up of 1991, several of the newly independent states have encouraged their native languages, which has partly reversed the privileged status of Russian, though its role as the language of post-Soviet national intercourse throughout the region has continued.

In Latvia, notably, its official recognition and legality in the classroom have been a topic of considerable debate in a country where more than one-third of the population is Russian-speaking, consisting mostly of post-World War II immigrants from Russia and other parts of the former USSR (Belarus, Ukraine). Similarly, in Estonia, the Soviet-era immigrants and their Russian-speaking descendants constitute about one quarter of the country's current population.