The Ainu (Japanese: アイヌ^?), also called Aynu, Aino (アイノ), and in historical texts Ezo (蝦夷), are an indigenous people in Japan (Hokkaidō) and Russia (Sakhalin and the Kuril Islands).

Historically, they spoke Ainu and related varieties. Most of those who identify themselves as Ainu still live in this same region, though the exact number of living Ainu is unknown. This is due to confusion over mixed heritages and to ethnic issues in Japan resulting in those with Ainu backgrounds hiding their identities. Intermarriage with Japanese has blurred the concept of a pure Ainu ethnic group. Official estimates of the population are of around 25,000, while the unofficial number is upward of 200,000 people.