Marriage in both Westeros and Essos is a religious ceremony. Though weddings are diverse in their exact customs and traditions, all involve the exchange of vows in the presence of particular sacred witnesses; such as a septon for the Faith of the Seven, a heart tree for the old gods, or a priest or priestess for the Drowned God or R'hllor. Following the ceremony, a feast is held, concluded by the bedding, which validates the marriage.
The head of house arranges betrothals for his family members. Marriages to girls who have not yet reached their majority or have not had their first flowering are rare, although they do occur. Once flowered, girls are deemed fit for bedding. In the Faith of the Seven, a marriage which has not yet been consummated can be annulled upon request to the High Septon or a Council of Faith. Once consummated, the marriage is considered to be valid. Though divorce is not common in Westeros, kings in both Westeros and Essos are able to set aside their wives.
Polygamy was practiced in Westeros before the Andal invasion. The Andals introduced Westeros to the Faith of the Seven, which considers polygamy to be a sin. Nevertheless, the rule of House Targaryen, whose members practiced the Valyrian custom of polygamy, was accepted in Westeros; for example, during the Conquest, offers of marriage were made to Aegon I Targaryen even though he already had two wives. Followers of the Drowned God on the Iron Islands practice a form of polygamous marriage where they can take multiple "salt wives" in addition to their "rock wife". Read more...