Group marriage combines polygamy and polyandry, though it may also be used as a loose term encompassing wife-exchange and a kind of sexual communism. The practice is generally incompatible with modernized society in its usual form. The breaking up of group marriage patterns by Western missionaries has been instrumental in causing the disintegration of traditional ethnic social structures. Where group sex is practised in developed society, it may cause adjustment problems or confusion of paternity. Wife-exchange may result in divorce or other marital problems.
Group marriage exists particularly among primitive tribes. It has also been found in societies where polyandry exists, such as India, Tibet and Sri Lanka. Certain African, Australian and New Guinea tribes practise a kind of sex communism, in which several men have the right of access to several women; but none of the women is properly married to more than one man. The existence of an early state of group marriage has been assumed from various customs, such as the lending or exchange of wives, sexual intercourse to which a girl is subject before her marriage, and the suspension of the ordinary rules of morality at certain ceremonies. Equivalents of group marriage in sophisticated society include wife-exchange, group sex, and particularly 'communes' or 'communities' where this is practised.