Kinslaying

"We are kin. Stark and Karstark.[...] Kill me and be cursed."

- Lord Rickard Karstark to King Robb Stark, his distant kin.

Kinslaying is the act of slaying a family member and a great taboo in the Seven Kingdoms. Whoever commits it is dubbed a kinslayer. Any individual who slays a member of their own family is believed to be cursed forever in the sight of gods and men.

Like incest or violating guest right, kinslaying is an abomination to every major religion in Westeros, including the Faith of the Seven, the Old Gods of the Forest, and the Drowned God.

The taboo associated with kinslaying is strong enough to stay the hand of even the most ruthless men. Tywin Lannister would have liked nothing more than to kill his son Tyrion the day he was born, because his mother died giving birth to him and for the shame he brought on their family for being born a dwarf. However, Tywin felt that House Lannister was above the shame and curse of kinslaying, so he relented and let Tyrion live.

Known and alleged kinslayers

 * King Aegon II Targaryen, who fed his sister Rhaenyra Targaryen to his dragon.
 * Ser Gregor Clegane, suspected to have murdered his young sister as well as his father.
 * Craster, who sacrifices his male offspring to the White Walkers.
 * Daenerys Targaryen stood by and allowed her husband Khal Drogo to execute her brother Viserys by pouring molten gold onto his head. This may not be considered an outright example of kinslaying, as Viserys had drawn a sword and threatened her within the Dothraki holy city of Vaes Dothrak, where drawing a sword is punishable by death (and Daenerys even warned Viserys as much). Thus, Drogo was within his rights to execute Viserys for this violation.
 * King Stannis Baratheon, who conceives a shadow assassin with Melisandre to kill his brother Renly.
 * Melisandre later insists to Stannis that she must sacrifice King Robert's bastard son Gendry. Stannis is uneasy about this and Davos Seaworth points out why: Gendry is his own nephew and he would be spilling his own blood. Davos concedes that Renly had wronged Stannis, declared himself king ahead of his older brother, stole his rightful bannermen to raise an army, and Renly himself would have killed his brother Stannis when their forces clashed on the battlefield. Renly was no innocent, but Gendry is just an innocent bastard boy. Once Davos verbalizes Stannnis' doubts, he agrees not to kill Gendry as it would be an unlawful kinslaying.
 * Ser Jaime Lannister, who murders Alton Lannister, his distant cousin, in his attempt to escape captivity.
 * King Robb Stark, is accused of it by Lord Rickard Karstark when the former is about to execute the latter. This was due to the distant blood ties between House Stark and House Karstark, and it is debatable if Robb would be officially labelled a kinslayer as a result.