The Caucasus region straddles the border between Europe and Asia and is dominated by the imposing Great Caucasus mountain range, which stretches between the Black Sea and the Caspian Sea and includes Europe's highest mountain, Mount Elbrus. This region has been known for a long time as one of the world's ethnically and linguistically most diverse areas. According to the Roman historian Pliny, when the Romans came to the Caucasus, they needed 134 interpreters to deal with the jumble of languages they found; the tenth century Arab geographer and historian al-Azizi referred to the area as the “mountain of languages”. Today, this relatively small area (about the size of New England) is home not only to over 100 languages, but to three distinct language families unique to the Caucasus region which have no kin elsewhere: the Northwest Caucasian family, the Northeast Caucasian family and the South Caucasian (or Kartvelian) family. These families are quite old, especially the South Caucasian and the Northeast Caucasian families (Nichols 1992: 14).

All three language families indigenous to the Caucasus are known for their complex systems of consonants (including some “exotic” consonants such as ejectives; see Section 4.2 below), complex agglutinative morphology and ergative case systems (see Section 3.2 above). These similarities led some linguists to consider those three families as branches of a larger Ibero-Caucasian macro family (this was originally proposed by a Georgian linguist, Arnold Chikobava); some other linguists – most notably a Russian historical linguist Sergei Starostin – believe that only Northwest Caucasian and Northeast Caucasian languages, are related. However, grammatical differences between the three groups of languages are considerable. For instance, even though all three groups have ergative systems of marking who did what to whom, they use very different morphological means to express such grammatical relations: Northeast Caucasian languages, such as Chechen, signal grammatical relations by case markers on nouns; Northwest Caucasian languages, such as Abkhaz, mark grammatical relations by complex agreement prefixes on verbs; and South Caucasian languages, such as Georgian, use both case markers on nouns and agreement markers on verbs. Moreover, while Northwest Caucasian languages such as Abkhaz inflect postpositions and possessed nouns, South Caucasian languages such as Georgian and Northeast Caucasian languages such as Chechen use a genitive case for possession. These differences force the more conservative historical linguists to treat the three language families of the Caucasus as unrelated.