Incest in the Bible

Incest in the Bible refers to sexual relations between certain close kinship relationships which are prohibited by the Hebrew Bible. These prohibitions are found predominantly in Leviticus 18:8-18 and 20:11-21, but also in Deuteronomy. The biblical categories of prohibited relationships does not entirely match the modern definitions of prohibited incestuous relations in force in various countries or of the various Christian denominations. (see Affinity (canon law) and Laws regarding incest.)

A few books of the Bible, particularly the early parts of the Torah, contain narratives in which certain individuals, from the same family as one another, engage in sexual intercourse together; while this could be construed as incest, endogamy is an alternative interpretation. The Bible does not, for example, forbid cousins from marrying, but it does prohibit sexual relations with several other close relatives.

In ancient times, tribal nations preferred endogamous marriage – marriage to one's relatives; the ideal marriage was usually that to a cousin, and it was often forbidden for an eldest daughter to even marry outside the family. Marriage to a half-sister, for example, is considered incest by most nations today, but was common behaviour for Egyptian pharaohs; similarly, the Book of Genesis portrays Sarah as marrying Abraham, her half-brother, without criticising the close genetic relationship between them, and the Book of Samuel treats the marriage of a royal prince to his half-sister as unusual, rather than wicked.

...
Wikipedia