Customs or laws regulating marriage following the death of a spouse, or in some cases during the lifetime of the spouse.
The levirate decrees a dead man's brother to be the widow's preferred marriage partner. In ancient Hebrew society, this practice served to perpetuate the line of a man who died childless. Often, the brother who marries his sister-in-law is a proxy for the deceased and no new marriage is contracted, since all progeny are acknowledged as the seed of the dead man. The sororate decrees the marriage of a man to his deceased wife's sister or, under so-called sororal polygyny, to the wife's younger sisters as they come of age. The latter was practiced by some American Indian tribes in the 19th century and continues among the Australian Aborigines .