In linguistics, an isolate (or language isolate) is a language that has no known genetic relatives.

It is unknown how it got where it did or how long it has been there; but often its isolation can be understood as its being the original language of the area (the substrate), and all its relatives having been submerged by a more recent wave of settlement or conquest.

Isolates in Europe are Basque and the extinct Etruscan. In Asia, there is ancient Sumerian, and there are Burushaski in the Himalayas, Nahali in eastern India, Andamanese of the Andaman Islands, Ainu of northern Japan, Korean, and Gilyak (Nivkh), Yeniseian (Ket), and Yukaghir all in Siberia but unconnected with each other.

In regions that are language-rich but less fully studied, there might not yet be the information to classify languages properly. So in New Guinea there are about 50 isolates, in northern Australian 13, and about a dozen in the Americas, but some of these may well belong to larger families.

North American isolates include Zuni, Keres, Kutenai, Tarasca, and the extinct languages Karankawa from Louisiana, Calusa from Florida, and Beothuk* from Newfoundland. South American isolates include Callahuaya, Aricapu, Baenna, Juma, and Natu.

Other languages, while not strictly isolates, belong to language families so small that they effectively are. For instance

Language classification is provisional. As well as the fact that some regions are less well studied, there is also an effort by some linguists to connect known language families into larger pictures, so we have hypothetical superfamilies like Nostratic, Dene-Caucasian, and Indo-Pacific. These often subsume some of the isolates. Into this category also falls the attempt to link Japanese and Korean with the smaller but still hypothetical Altaic family.
* Thanks to Cletus the Foetus for the information that Beothuk is now believed to have been an Algonkian language.