In most of Africa, marriage is more a of union between two lineages or families than it is a union between the individual husband and wife. Marriage is undertaken for many reasons, but the primary ones are to provide legitimate successors to status and inheritors of property rights and to form alliances and ties between clans and other units, in order to knit them into a single society.
Incest within certain degrees of kinship is everywhere forbidden. Exogamy, the prohibition of marriage within certain descent groups, is typically practiced with regard to clan and other basic social units, such as those of the tribe and settlement. Endogamy is found in some societies, those in which there are political or mercantile elites that prefer to retain power and wealth within their own hands through marriages among themselves.
A crucial factor in any marriage arrangement is whether patrilineal, matrilineal, or cognatic groups form the basic social structure. In patrilineal systems, marriage is typically sealed by the transfer of property, known as bride-wealth, usually in the form of cattle. The husband's group transfers property to that of the wife, in return for the transfer to them of rights of procreation and sexuality on the part of the wife from those who have been her guardians (e.g., her father or her brothers). Usually, if divorce later occurs, the bride-wealth must be returned, less a proportion for each child who remains with the husband's group. There are many variations, but this simple principle generally holds true. In matrilineal societies, bride-wealth is not transferred because the children belong to the wife's clan or lineage and will inherit from that group; the husband's heirs are his sisters' children, and his own children inherit from his wife's brothers, their maternal uncles. There is no need for bride-wealth, as rights in a woman's children are not transferred, although small gifts are always presented, and the husband may have to work for his wife's parents for some time.
Residence after marriage is linked to several factors. In patrilineal systems, it is nearly always virilocal, with the wife living in her husband's natal settlement and being regarded as a "stranger" until she has borne children to his group. In matrilineal systems, residence may be virilocal, or it may be uxorilocal, in which case the husband goes to live with his wife's relatives and remains a "stranger" in that settlement. With uxorilocal residence in particular, the husband's position is often ambivalent, and divorce is more frequent. In many places, however, especially in urban centers, residence after marriage is increasingly becoming neolocal: the husband and wife establish their own home, away from those of either set of parents.
Polygyny has traditionally been the ideal. It is rare, however, for more than a quarter of the men in a community to have more than one wife, and a man's later wives are frequently those inherited from a senior deceased kinsman (by the institution of the levirate or by widow inheritance). In many societies, women marry at puberty, but men marry in their thirties or even later. This makes polygyny possible because by then there are fewer marriageable men, as many will have died from natural causes or from warfare.