Ainu is a dormant language isolate previously spoken on the northernmost Japanese island of Hokkaido, as well as southern half of the Russian island of Sakhalin, and in the disputed Kuril Islands. There have been a large number of proposed relationships between Ainu and other language families. While most of the claims with regards to a genetic relationship are questionable, language contact between Ainu and Japanese on the one hand and Ainu and Nivkh on the other are well-substantiated, albeit understudied. There are several grammars of Ainu. The early Japanese-language grammars are short but are still valuable due to the fact that the authors were in consultation with native speakers. There are a number of collections of Ainu materials. Two of the most notable collections are Kindaichi and Kannari and Izutsu. Ainu is primarily divided into three groups: varieties found on Hokkaido, varieties found in the Kuril Islands, and varieties found on Sakhalin Island.