Russian is an East Slavic language and an official language in Russia, Belarus, Kazakhstan, Kyrgyzstan and many minor or unrecognised territories throughout Eurasia (particularly in Eastern Europe, the Baltics, the Caucasus, and Central Asia). It is an unofficial but widely spoken language in Latvia, Moldova, Ukraine and to a lesser extent, the other post-Soviet states.

Russian belongs to the family of Indo-European languages and is one of the four living members of the East Slavic languages (which in turn is part of the larger Balto-Slavic branch). Written examples of Old East Slavonic are attested from the 10th century onward.

It is the most geographically widespread language of Eurasia and the most widely spoken of the Slavic languages (followed by Polish and then Ukrainian). It is also the largest native language in Europe, with 144 million native speakers in Russia, Ukraine and Belarus. Russian is the eighth most spoken language in the world by number of native speakers and the seventh by total number of speakers. The language is one of the six official languages of the United Nations. Russian is also the second most widespread language on the Internet after English.

Russian distinguishes between consonant phonemes with palatal secondary articulation and those without, the so-called soft and hard sounds. Almost every consonant has a hard or a soft counterpart, and the distinction is a prominent feature of the language. Another important aspect is the reduction of unstressed vowels. Stress, which is unpredictable, is not normally indicated orthographically though an optional acute accent may be used to mark stress, such as to distinguish between homographic words, for example замо́к (zamók, meaning a lock) and за́мок (zámok, meaning a castle), or to indicate the proper pronunciation of uncommon words or names.

Russian is one of the official languages of United Nations. In March 2013 it was announced that Russian is now the second-most used language on the Internet after English. People use the Russian language on 5.9% of all websites, slightly ahead of German and far behind English (54.7%). Russian is used not only on 89.8% of .ru sites, but also on 88.7% of sites with the former Soviet Union domain .su. The websites of former Soviet Union nations also use high levels of Russian: 79.0% in Ukraine, 86.9% in Belarus, 84.0% in Kazakhstan, 79.6% in Uzbekistan, 75.9% in Kyrgyzstan and 81.8% in Tajikistan. However, Russian is the sixth-most used language on the top 1,000 sites, behind English, Chinese, French, German and Japanese.