Oathbreaking

"So many vows. They make you swear and swear... Defend the king, obey the king, obey your father, protect the innocent, defend the weak. But what if your father despises the king? What if the king massacres the innocent? It's too much. No matter what you do you're forsaking one vow or another."

- Ser Jaime Lannister

Oathbreaking is the direct violation of an oath, and a serious crime in Westeros. Those who belong to monastic orders take explicitly religious vows. Even the bonds between secular lords and their vassals are typically backed by religious oaths. Oathbreaking is therefore considered not only a crime but a sacrilege, breaking holy vows - though some sets of vows are considered more sacrosanct than others.

Members of the Night's Watch, the Maesters, the Kingsguard, and the religious orders of the Faith of the Seven all swear holy oaths promising a lifetime of obedience, chastity, and a rejection of any previous family ties or claims to inheritance.

The penalty for oathbreaking is often death, though this may depend on the severity of the oath broken. Secular lords who rise up in rebellion but who then surrender are often forgiven (to encourage them to surrender). At other times, high treason is punished with execution. Septons of the Faith of the Seven or Maesters who break their vows are often simply expelled from their orders.

The Night's Watch, however, operates under a strict code that oathbreaking, particularly desertion, will be punished by death. In practice, due to the declining numbers and stretched resources of the Watch, officers will usually turn a blind eye if some men ride off to the nearby settlement of Mole's Town to have sex with prostitutes now and again. Also if a recruit attempts to desert, but changes his mind on the road and quickly returns, their leaders will often pretend that no harm was done.

Regicide is considered an extreme form of oathbreaking, particularly for a king to be killed by his own personal bodyguard. The Kingsguard swear the holiest of vows to serve and defend the life of their king. Thus it was considered shocking when the Kingsguard Jaime Lannister slew King Aerys II Targaryen at the climax of Robert's Rebellion.

Oathbreaking, even regicide, is still not considered quite so despicable as Kinslaying, or worst of all, violating guest right. Breaking guest right could itself said to be the most utter, extreme form of oathbreaking: violating the basic social promise that guest and host will not harm each other while under the same roof. Meanwhile, oathbreaking is considered worse than the shame of bastardy.

While the Faith of the Seven is the dominant religion in Westeros, it never entirely replaced the Old Gods of the First Men, which is still the majority religion in the North. Therefore many oaths are often sworn by "both the Old Gods and the New" (that is, the Seven). The Iron Islands also worship a third, local religion devoted to the Drowned God. Men and women typically swear by whatever religion they personally follow.

Officially, it is impossible to force anyone to take holy vows, and oaths made only under duress are not considered binding in the sight of the gods. That being said, there have been many instances in which daughters of noble families were forced against their will to enter into arranged marriages to secure political alliances. Such alliances will, however, at least outwardly pretend that the match is consensual, forcing the bride (or in some cases, groom) to physically utter the oaths during the wedding ceremony.

Particular cases of Oathbreaking

 * Despite his marriage to Elia Martell, Rhaegar Targaryen broke his oath when he abducted Lyanna Stark, who was betrothed to Robert Baratheon.
 * Ser Jaime Lannister, who betrayed his oaths as a Kingsguard and slew King Aerys II Targaryen during the Sack of King's Landing, to prevent him from carrying out his wildfire plot and destroy the city of King's Landing, earning the nickname of "Kingslayer" because he kept his reason a secret. Pardoned by King Robert Baratheon.
 * Despite his marriage to Cersei Lannister, Robert Baratheon broke his oath with his constant whoring. Meanwhile, Cersei also broke her oath by continuing an illicit, incestuous relationship with her twin brother Jaime Lannister.
 * Despite his marriage to Catelyn Stark, Eddard Stark fathered a bastard son, Jon Snow, with a woman named Wylla.
 * Mance Rayder, who deserted his post as a Ranger of the Night's Watch to live among the Free Folk and install himself as King-beyond-the-Wall.
 * Will, a Ranger of the Night's Watch, deserted his post after witnessing an attack by the White Walkers. Beheaded by Eddard Stark.
 * The Mutineers, led by Rast and Karl Tanner, who mutinied against Lord Commander Jeor Mormont. All were slain during the Raid on Craster's Keep.
 * Robb Stark, King in the North, broke an oath made on his behalf by his mother Catelyn Stark to marry any eligible daughter or granddaughter of a crucial ally Walder Frey, choosing instead to marry Talisa Maegyr. Lord Walder retaliated against the Starks by having Robb, Catelyn, and a pregnant Talisa killed along with most of their bannermen and men-at-arms in a horrific massacre called the Red Wedding after luring the Starks into a false sense of security by extending them guest right.
 * Roose Bolton, who betrayed his oaths as a bannerman of House Stark and personally slew Robb Stark at the Red Wedding, in exchange for rulership of the North.
 * The Mutineers, led by Alliser Thorne, who mutinied against Lord Commander Jon Snow. Thorne was later hanged along with Olly, Othell Yarwyck, and Bowen Marsh by Snow himself.
 * The Sand Snakes, led by Ellaria Sand, who betrayed their oaths to Prince Doran Martell by murdering him and his son Prince Trystane Martell.

Acts considered Oathbreaking

 * Desertion
 * Adultery
 * Violations of guest right are also considered a form of oathbreaking as hosts swear a holy oath to protect their guests for the duration of their stay. Likewise, guests are also expected to uphold the same oath.
 * Regicide
 * Knights take sacred oaths to defend the innocent and protect the weak. However, due to their oaths of obedience, and the social abyss between nobility and smallfolk, knights often find themselves doing the exact opposite to their vows, particularly in times of war. Unless they find themselves on the losing side of the war, these knights will seldom be branded oathbreakers and face justice.
 * The refusal of a vassal, regardless of their station, to answer the summons of their liege lords, are considered acts of oathbreaking and even treason.

Quotes
"I know I broke my oath. I know I'm a deserter."

- Will

"Every girl in the Seven Kingdoms dreamed of him, but he was mine by oath."

- Cersei Lannister on her unfaithful husband Robert Baratheon.

"Some men take their oaths more seriously than others."

- Catelyn Stark

"My sword is yours, in victory and defeat, from this day until my last day."

- Theon Greyjoy swears an oath, that he would eventually break, to Robb Stark.

"You swore some vows, I want you to break them."

- Ygritte to Jon Snow

"Tell me, if your precious Renly commanded you to kill your own father and stand by while thousands of men, women, and children burned alive, would you have done it? Would you have kept your oath then?"

- Jaime Lannister to Brienne of Tarth

"When I was your age, I'd have broken fifty oaths to get into that."

- Walder Frey to Robb Stark

"You already swore me one oath, right here in my castle. You swore by all the gods that your son would marry my daughter!"

- Walder Frey hypocritically faults the Starks for breaking an oath they made to him.

"The Red Wedding, they're calling it. Walder Frey committed sacrilege that day. He shared bread and salt with the Starks. He offered them guest right. The Gods will gave their vengenance. Frey will burn in the Seventh Hell for what he did."

- Farmer curses Walder Frey.

"Elia loved him. She bore his children. Swaddled them, rocked them, fed them at her own breast. Elia wouldn't let the wet nurse touch them. And beautiful, noble Rhaegar Targaryen...left her for another woman."

- Oberyn Martell on his unfaithful brother-in-law Rhaegar Targaryen.