Isolate languages are often the subject of intensive studies in order to attempt proof of genetic relationships between languages. Basque, for instance, has been the subject of comparisons to the South Caucasian languages and the Indo-European language family.
Some languages are isolates because all the other languages in that language family have died. The Pirahã language of Brazil is one such language, the last language alive belonging to the Mura family. In contrast, there are languages whose relatives are spoken by communities a long distance away, because of past migrations. Such languages are not considered isolates.
Below is a list of known language isolates, along with notes on possible relations to other languages or language families:
| Language | Comments |
| Ainu | Endangered language. |
| Basque | No known relatives. Some linguists have attempted to show relationship with the Caucasian languages or Iberic. |
| Burushaski | Little information available. |
| Etruscan | Not well understood at present |
| Gilyak | or Nivx. A Palaeosiberian language spoken in the lower Amur basin and on Sakhalin; Ainu is also spoken on Sakhalin. |
| Iberic | There are lexical coincidences with Basque, but it is hard to know if they are more than a result of vicinity. |
| Ket | No known relatives. Some linguists have attempted to show a relationship with Burushaski. |
| Japanese | Possibly related to Korean language, though not yet proven. Connections to the Altaic languages have also been proposed. |
| Korean | Possibly related to Japanese language, though not yet proven. Connections to the Altaic languages have also been proposed. |