The Slavic languages (also called Slavonic languages), a group of closely related languages of the Slavic peoples and a subgroup of Indo-European languages, have speakers in most of Eastern Europe, in much of the Balkans, in parts of Central Europe, and in the northern part of Asia.

The imposition of Church Slavonic on Orthodox Slavs was often at the expense of the vernacular. Says W.B. Lockwood, a prominent Indo-European linguist: "It O.C.S remained in use to modern times, but was more and more influenced by the living, evolving languages, so that one distinguishes Bulgarian, Serbian, and Russian varieties. The use of such media hampered the development of the local languages for literary purposes and when they do appear the first attempts are usually in an artificially mixed style." (148) Lockwood also notes that these languages have "enriched" themselves by drawing on Church Slavonic for the vocabulary of abstract concepts. The situation in the Catholic countries, where Latin was more important, was different. The Polish Renaissance poet Jan Kochanowski and the Croatian Baroque writers of sixteenth century all wrote in their respective vernaculars (though Polish itself had drawn amply on Latin in the same way Russian would eventually draw on Church Slavonic).

Although the Church Slavonic language hampered vernacular literatures, it nonetheless fostered Slavonic literary activity and abetted linguistic independence from external influences. The languages of the Catholic Slavs tottered precariously near extinction on many occasions. The earliest Polish is attested in the fourteenth century; before then, the language of administration was Latin. Czech was always in danger of giving way to German, and Czech's relatives Upper and Lower Sorbian, spoken only in Germany, have nearly succumbed just recently. Under German and Italian influence for many centuries, the Slovene language was a regional language spoken by peasants, and was brought to written standards only by the followers of the Reformation in the 16th century. Only the Croatian vernacular literary tradition matches Church Slavonic in age. It began with the Vinodol Codex and continued through the Renaissance until the codifications of Serbo-Croatian in 1850, though much of the literature between 1300 and 1500 was written in much the same mixture of the vernacular and Church Slavonic as prevailed in Russia and elsewhere. The independence of Ragusa facilitated the continuity of the tradition.

More recent foreign influences follow the same general pattern in Slavic languages as elsewhere, and are governed by the political relationships of the Slavs. In the seventeenth century, bourgeois Russian (delovoi iazyk) absorbed German words through Polish. In the Petrovian era, close contacts with France invited countless loans and calques from French, a significant fraction of which not only survived, but replaced older Slavonic loans. Russian, in turn, influenced most literary Slavic languages by one means or another in the nineteenth century. Croatian writers borrowed Czech words liberally, whereas Czech writers, scrambling to revive their dying language, had in turn borrowed many words (cf. vzduch, air) from Russian. A more direct role for Russian came vis-a-vis Bulgarian, where Russian words were imported en-masse to replace Turkish and Greek loans, so that many Bulgarian words now carry a Russian phonetic footnote (i.e., have a phonetic structure unusual for the Bulgarian language or, indeed, the South Slavic languages in general).