The Ainu or in historical Japanese texts Ezo; are an indigenous people of Japan (Hokkaido; and formerly northeastern Honshu) and Russia (Sakhalin and the Kuril Islands).

Historically; they spoke the Ainu language and related varieties and lived in Hokkaido; the Kuril Islands; and much of Sakhalin. 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.

In Japan; because of intermarriage over many years with Japanese; the concept of a pure Ainu ethnic group is no longer feasible. Official estimates of the population are of around 25;000; while the unofficial number is upward of 200;000 people.