History Main / BloodOath

In one common version, Al and Bob become BloodBrothers, cutting their hands open and shaking on the deal. (DontTryThisAtHome; these rituals carry a [[JustForFun/TelevisionIsTryingToKillUs risk of transmitting bloodborne infections like hepatitis and HIV]].) A lighter version is the SpitShake.

* In ''Film/{{Mongol}}'' young Temudgin (the future UsefulNotes/GenghisKhan) makes a blood oath with Jamukha, who saved his life. They become BloodBrothers, complete with slicing their palms and letting the blood drip into a bowl of milk that they drink. [[spoiler:In the end, Temudgin lets Jamukha go, even though he proves to be a threat in the future, saying that he's not sparing an enemy, he's freeing his brother.]]

* ''Film/TheOutlawJoseyWales'' and Ten Bears take a blood oath to seal the "words of iron" peace treaty between the Comanches and Josey's friends at the Turner Ranch and Santo Rio. It is strongly implied, though unstated, that this also makes Josey and Ten Bears BloodBrothers.

In one common version, Al and Bob become BloodBrothers, cutting their hands open and shaking on the deal. (DontTryThisAtHome; these rituals carry a [[JustForFun/TelevisionIsTryingToKillUs risk of transmitting bloodborne infections like hepatitis and HIV]].)

!This trope is [[https://tvtropes.org/pmwiki/posts.php?discussion=17000755720.98896700 under discussion]] in the Administrivia/TropeRepairShop.

* In ''Literature/ShadowsForSilenceInTheForestsOfHell'', by Creator/BrandonSanderson, shedding blood will draw the wrath of the shades like nothing else. An accidental bump or nosebleed doesn't count, but blood shed in anger, exposed to the air, will enrage every shade in the vicinity. First, they will hunt down and kill whoever shed the blood, then, being enraged, they'll kill anyone else that happens to be nearby.

* ''Series/HouseOfTheDragon'' has an interesting example. A Valyrian wedding ceremony merges classic wedding vows with a blood oath. When Rhaenyra proposes to Daemon she says it with the phrase, "Let us bind our blood." The ceremony involves them cutting their palms and clasping their bleeding hands, as well as painting marks onto each other's foreheads in blood. Lastly they cut their bottom lips and kiss with bloody mouths.

*** It should also be noted that "Start of Darkness" depicts taking the Oath much like getting a tattoo. Including the part where [[spoiler:Eugene]] [[AlcoholInducedIdiocy got it while he was smashed]] and had little recollection of doing so later.

* In ''WesternAnimation/WereBackADinosaursStory'', this is how Louie and Cecilia join Professor Screweyes' circus. At first the contract is blank, but once the Professor pricks Louie's finger with his pen and the drop of blood touches the paper, it magically fills out, with the blood stain turning into Louie's signature. Cecilia then does the same by pricking her own finger with a hair pin.

*** It should also be noted that "Start of Darkness" depicts taking the Oath much like getting a tattoo. Including the part where Eugene [[AlcoholInducedIdiocy got it while he was smashed]] and had little recollection of doing so later.

[[folder: Western Animation]]

-->'''Bubbles:''' I like the red ink.
-->'''HIM:''' Uh...Yeah...Ink.

-->'''Wizard:''' Just bleed ''here'', and ''here''.
-->'''Rick:''' I'm not cobleeding.

* It's explicitly said in ''Manga/ChronoCrusade'' that when Chrono [[DealWithTheDevil made a contract]] with [[spoiler:Mary Magdalene, his first contractor]], that she had to give him some of her blood to complete it. It's implied (using vampire imagery) that this was also the case with his contract with Rosette.

In another, Al cuts his hand open, and simply lets the blood drip to the ground. This is sometimes highlighted by the phrasing of the oath: "If I break my word may the Earth drink my blood!" Then giving the Earth a 'taste' of your blood so that it knows what to look for if you fail to keep your oath. Sometimes this version is used to swear an oath of vengeance- and making it clear that you mean business.

* ''/Literature/StarWarsBloodline'': One of the few duties of the Supreme Governor of Birren is to take an oath to keep items under royal seal secret even unto death. When the childless Lord Mellowyn dies, the Governorship was supposed to go to Princess Leia as she was next in line but she stepped aside in favor of Lady Carise Sindian. Sindian breaks her [[TheOathBreaker oath]] when she finds a music box containing a message from Bail Organa about Leia's biological father. Leia declines to prosecute this violation to the full extent that she could, but does [[BestServedCold convinces]] the Elder Houses to strip Sindian of her Governorship and her royal titles.

* In Literature/TheBible, the covenants that God makes with His people require the shedding of blood to make them effective and binding. Moses sprinkled the book of the Mosaic Covenant as well as the Israelites with the blood of goats and calves to sign and seal that covenant. Years later, Jesus would shed His blood on the cross to put into effect the New Covenant between God and His people, the Christians.

* In ''TabletopGame/{{Ironsworn}}'', an iron vow is the equivalent of a blood oath. On top of that, [[PlayerCharacter Ironsworn]] can choose to vow with literal blood.

* Starting with 4th Edition, some of the Triad gangs in ''Tabletopgame/{{Shadowrun}}'' have started swearing blood oaths that are magically binding, resulting in DeathOfAThousandCuts if they violate those oaths (particularly the oath of secrecy).
* Creator/WhiteWolf:

** ''TabletopGame/ChangelingTheLost'' has many forms of oaths, and your health or life can be put on the line for them. With heavy costs comes heavy rewards - the more you'll lose if you break the oath, the more benefit you can gain from it.

* In one episode of ''WesternAnimation/ThePowerPuffGirls2016,'' Bubbles and Buttercup sell Blossom's soul to HIM for a dollar, and this trope is implied when the girls sign the contract that HIM gives them.

** It's later revealed that Swan was offered a DealWithTheDevil, who was the first to ask for this. Swan uses the razor he was originally planning to kill himself with, and Satan quips, "Either way, you're mine."

* JustForFun/RecycledInSpace for the ''Literature/{{Boojumverse}}'' tale "The Wreck of the Charles Dexter Ward" with the protagonist providing both a thumbprint and DNA sample to seal a contract. There's a DealWithTheDevil feel to it as well, as she's been given a TooGoodToBeTrue offer that she's not in a position to refuse.
-->He slid a tablet across the rented desk. Cynthia pressed her thumb against it; a prick and a buzz, and her blood and print sealed the contract.

-->Just as she had when she took Captain Song’s oath and slit her thumb with a razorblade and dripped her blood on the Lavinia Whateley’s decking so the ship might know her, Black Alice—metaphorically speaking—took a breath and jumped.

* An episode of ''Series/StarTrekDeepSpaceNine'' is actually titled "[[Recap/StarTrekDeepSpaceNineS02E19BloodOath Blood Oath]]". In it, Dax is called upon to fulfill a vow of vengeance [[TheNthDoctor her previous self]] made with three Klingon friends twenty-five years ago.

* RecycledInSpace for the ''Literature/{{Boojumverse}}'' tale "The Wreck of the Charles Dexter Ward" with the protagonist providing both a thumbprint and DNA sample to seal a contract. There's a DealWithTheDevil feel to it as well, as she's been given a TooGoodToBeTrue offer that she's not in a position to refuse.

* BloodOath: In ''TabletopGame/{{Ironsworn}}'', an iron vow is the equivalent of a blood oath. On top of that, [[PlayerCharacter Ironsworn]] can choose to vow with literal blood.

* The card [[http://gatherer.wizards.com/Pages/Card/Details.aspx?multiverseid=205118 Sign in Blood]] from ''TabletopGame/MagicTheGathering''. Apparently it's quite a long document, because it hurts as much as getting mauled by a bear.

** ''TabletopGame/VampireTheRequiem'' has the Invictus (a covenant of fedualist vampires heavy on inherited power) and their Blood Oaths, magical bonds with ''heavy'' penalties for violation.

Can overlap with CouldntFindAPen, which is any kind of writing in blood. Contrast with HeroicVow. See also {{Geas}}. May or may not involve actual BloodMagic. When someone has broken this vow so thoroughly they become ostracised they're TheOathBreaker.