In The Bible
The Bible lists several types of relationship which it regards as incestuous unions; one list appears in Deuteronomy, and two lists occur in the Book of Leviticus. These lists only mention relationships with female relatives; excluding lesbianism, this implies that the list is addressed to men. Since the lists would then describe women with whom it is forbidden for a man to have a relationship, they also indirectly imply a list of men with whom it is forbidden for a woman to have a relationship. These lists then compare as follows (blue = forbidden for men only, pink = forbidden for women only, purple = forbidden for both men and women):
| Leviticus 18 | Leviticus 20 | Deuteronomy | |||
| Grandparent's spouse (including other grandparent) | |||||
| Parent's spouse | Parent | ||||
| Stepparent | |||||
| Parent-in-law | |||||
| Uncle/Aunt | Parent's sibling | ||||
| Uncle's/Aunt's Spouse | Father's sibling's spouse | ||||
| Mother's sibling's spouse | |||||
| Parent's child | Half-Sibling (mother's side) | ||||
| Father's child | Sibling | ||||
| Half-Sibling (father's side) | |||||
| Step sibling | |||||
| Sibling-in-law (if the spouse was still alive) | |||||
| Nephew/Niece | Sibling's child | ||||
| Nephew/Niece-in-law | Spouse's Brother's Child | ||||
| Spouse's Sister's Child | |||||
| Spouse's child | Child | ||||
| Stepchild | |||||
| Child-in-law | |||||
| Spouse's grandchild (including grandchild) | |||||
One of the most notable features of all the lists is that sexual activity between a man and his own daughter is not explicitly forbidden, although the first relation mentioned after the Levitical prohibition of sex with "near kin" is that of "thy father." The Talmud argues that this absence is because the prohibition was obvious, especially given the proscription against a relationship with a granddaughter. As with the case of a man's own daughter, the shortness of the list in Leviticus 20, and especially of that in Deuteronomy, are explained by classical Jewish scholarship as being due to the obviousness of the missing prohibitions.
Apart from the case of a man marrying his daughter, the list in Leviticus 18 roughly produces the same rules as were followed in early (pre-Islamic) Arabic culture. However, most tribal nations also disliked exogamous marriage - marriage to completely unrelated people.
Judaism's view is that prior to the giving of the Torah at Mount Sinai, some of the prohibitions only applied voluntarily. Thus in several prominent cases in the Torah, the incest rules are ignored in favour of marriage to a close relative; Jacob is described as having married his first wife's sister.
Read more about this topic: Jewish Views On Incest