The Ainu people had various types of marriage. A child was promised in marriage by arrangement between his or her parents and the parents of his or her betrothed or by a go-between. When the betrothed reached a marriageable age, they were told who their spouse was to be. There were also marriages based on mutual consent of both sexes. In some areas, when a daughter reached a marriageable age, her parents let her live in a small room called "tunpu" annexed to the southern wall of her house. The parents chose her spouse from men who visited her.
There are some basic features of sociopolitical organization that are shared by most of the Ainu groups, although their finer workings vary from region to region. Among most Ainu groups, the nuclear family is the basic social unit, although some extended families are present. In most Ainu settlements, males related through a common male ancestor comprise the core members who collectively own a hunting ground or a river with good fish runs. Although some scholars emphasize that among the Ainu along the Saru River in Hokkaidō women related through females comprise a corporate group, the exact nature of the group is unclear. Among these Hokkaidō Ainu, an individual is prohibited from marrying a cousin on his or her mother's side. Among most Ainu groups, a few prominent males in the community practice polygyny.
History, population fluctuation details (largely due to harsh effects of colonization).