Vendetta is a term for blood feud where relatives of someone who have been killed or otherwise wronged seek vengeance trying to kill or otherwise punish the ones responsible or their relatives. The original word originates from Latin vindicta ("vengeance").

Originally vendetta referred to a blood feud between two families or bloodlines where kinsmen of the killed person intended to avenge the death by killing either those responsible for the killing or some of their relatives. The responsibility to maintain the vendetta usually falls on the person who is closest male relative to whoever has been killed or wronged but other members of the family may take the mantle as well. If the culprit had disappeared or was already dead, the vengeance could extend to other relatives.

Vendetta originated from historical societies with no central government (or where the central government did not consider itself responsible for mediating this kind of disputes) where family and kinship ties were the main source of authority. In effect, the whole family was though to be responsible to whatever one of them had done. Sometimes even two separate branches of the same family could come to blows over some matter. The practice is thought to have disappeared with more centralized societies where law enforcement and criminal law take responsibility of punishing the lawbreakers.

Vendetta is reputedly still practiced in some areas in Corsica, Italy — especially Sardinia, Sicily and Calabria — as well as Crete in Greece, where those seeking retribution do not accept or respect local law enforcement authority. They may think that law enforcement is either disinterested about their affairs or possible biased to protect their opposition and in effect rely on vigilantism.

In Japan's feudal past the Samurai class upheld the honor of their family, clan, or their lord by katakiuchi (敵討ち), or revenge killings. These killings could also involve the relatives of an offender.

Mutual vendetta may develop into a vicious circle of further killings, retaliation, counterattacks and all-out warfare that can last to the mutual extinction of both families. The primary reason for the enmity might have actually disappeared over time.

Traditions similar to vendetta have existed almost anywhere, like between various Arabic people, Albanians and Circassians. Some of the gang wars between organized crime groups are effectively forms of vendetta, where the criminal organization (like Mafia "family") has taken the place of relatives.

In the modern parlance the term is sometimes extended to mean any other long-standing mutual quarrel, disagreement or rivalry. One political party may state that the other party is pursuing, for example, investigation of some matter as a form of political vendetta.

For the computer game, see Vendetta (game)