While cousin marriage is legal in most, and avunculate marriage is legal in many countries, sexual relations between siblings is considered incestuous almost universally.

After her death in 612, he married his niece Martina in 613; this second marriage was considered incestuous and was very unpopular.

Under South Korea's Family Law, which bans marriage between men and women with both the same name and the same ancestral village, their relationship was considered incestuous.

Snokachestvo was considered incestuous by the Russian Orthodox Church and unseemly by the obschina, the rural community.

In anime and manga, cousin coupling is very common, this because cousin marriages are not considered incestuous, but actually have been desirable in Japan.

Zoroastrian "self-marriages", that were considered incestuous under sharia, were also tolerated.

Rumors that Isabeau and Orléans were lovers began to circulate, a relationship that was considered incestuous.

In Roman society, an uncle (Claudius) marrying his niece (Agrippina) was considered incestuous, and obviously immoral.

Those marriages, if discovered, would be considered incestuous under Utah consanguinity laws.

She never expresses her feelings, either, about the morality of marrying her brother-in-law, though this was considered incestuous at the time.