WIKIPEDIA : RELIGIOUS VIEWS ON INCEST

Religious views on incest

[edit] Judeo-Christian
Main article: Biblical References to Incest
In the story of Sodom and Gomorrah in the Book of Genesis in the Bible, Lot's two daughters have sex with him to carry on their lineage.
Later, the Book of Leviticus lists prohibitions against sexual relations between various pairs of family members. Father and daughter, mother and son, and other pairs are forbidden, on pain of death, to have sexual relations. (Father–daughter incest is covered by a prohibition on sexual relationships between a man and any daughter born to any woman he has had sexual relationships with, thereby prohibiting his incest not only with his own daughters but also with women who could be his stepdaughters by marriage.)

[edit] Islam
The Quran mentions incest which prohibits a man from having sexual relationships with his mother, daughter, sister, paternal aunt, maternal aunt or niece. However, Islam allows for marriage with cousins and other more distant relatives. Only in case of marriage does Islam allow sexual relations between cousins and other distant relatives.

[edit] Hinduism
Hinduism speaks of incest in highly abhorrent terms. Hindus were greatly fearful of the bad effects of incest and thus practice to date strict rules of both endogamy and exogamy, that is, marriage in the same caste (varna) but not in the same family tree (gotra) or bloodline (Parivara). Marriages within the gotra ("swagotra" marriages) are banned under the rule of exogamy in the traditional matrimonial system. People within the gotra are regarded as kin and marrying such a person would be thought of as incest.
In some South Indian communities, where gotra membership passed from father to children, marriages were allowed between uncle and niece, while such marriages were forbidden in matrilineal communities, like Malayalis and Tuluvas, where gotra membership was passed down from the mother. A much more common characteristic of south Indian Hindu society is permission of marriage between cross-cousins (children of brother and sister). Thus, a man is allowed to marry his maternal uncle's daughter or his paternal aunt's daughter but is not allowed to marry his paternal uncle's daughter, a parallel cousin, who is treated as a sister.
North Indian Hindu society not only follows rules of gotra for marriages, but also has many regulations which go beyond the basic definition of gotra which result in few occurrences of similarly incestuous relationships.

[edit] http://en.wikipedia.org/wiki/Incest