The nuclear family, which consists of a husband and wife, or wives, and children, is the basic social unit of Kikuyu society. As children grow up and form their own families, a subclan ( mbari ) is formed. Each mbari contains a hundred to a thousand families, and each member of an mbari knows from which ancestor, or which daughter of Kikuyu and Mumbi, they originate. The Kikuyu family is considered to be circular, rather than linear as in Western cultures. Each new generation replaces their grandparents, who are then free to become ancestors. The need to replace four grandparents is an important reason for having a minimum of four children, and more children gives honor to the parents' siblings.
Extended families living together form a homestead ( mucii ; pl. micii ), and several micii together form into larger units, roughly equivalent to villages or hamlets.
Ideally, the mucii includes the paternal head of the family, his wives or wife, their unmarried children, often his married sons, and sometimes single male or female relatives. The Kikuyu are traditionally polygynous, but with the influence of Christianity and Western education, the trend has been toward monogamy. If a man chooses to marry more than one wife, theoretically he must provide ruracio (bride-wealth) and a separate house for each within the homestead.