• Northwest languages or Abkhaz-Adygh languages

e.g. Circassian[?], Abkhaz

• Northeast languages or Dagestan languages

e.g. Avar, Daghi (Dargwa), Lezgian

• North Central languages or Nakh languages or Vaynakh languages

e.g. Chechen

The last two groups sometimes are called Nakh-Dagestan languages. They have a number of common features in phonetics and grammar, for example, ergative case and sentence structure, but their genetic relationship is not clear. In addition to these peculiarly Caucasian languages, there are linguistic 'islands' of Indo-European (e.g. Persian(Ossetian) and Armenian) and Altaic (e.g. Turkish(Azeri), Tatar(Karachai-Balkar, Nogai and Kumik) and Mongol(Kalmyk) at the mouth of the Volga)

South Caucasian[?] and North Caucasian[?] are two distinct, unrelated phyla even in Greenberg's classification. Generally, the former are spoken south of the Caucasus and the latter north of the Caucasus watershed. North Caucasian[?] split in two about five thousand years ago giving rise to the northwest or Pontic group comprising: Circassian[?] (= Adyghe + Kabard-Cherkess), Ubykh and Abxaz[?] or Abkhaz; and the northeast or Caspian group which early split into western, central and southern branches. The western branch divided early into Nakh and Avar-Andi-Dido. The chief extant languages of these two are Chechen and Avar respectively. The central branch gave rise to Lak[?] and Dargwa[?], the southern branch to Lezgi[?] and Xinalux[?] or Khinalugh.

Udi[?] is an aberrant form of Lezgi[?] and Dido[?] an aberrant form of Avar[?].

The Caucasus has the largest concentration of ergative languages in Europe. All of these language families are characterised by an ergative system; also, they tend to be verb-focused, with much information about nouns encoded in the verb.