Marriages are frequently preceded by a betrothal. Betrothals are expected to be arranged by the head of a house, both for his or her children and any unwed younger siblings. There is no age limit to betrothals or marriages. Children might be as young as two years old when betrothed although generally, children are somewhat older. Marriages to girls who have not yet reached their majority or even their first flowering (i.e., has had her first menstruation) do happen, although not often. Usually, the bride has already reached her majority, or is even older, although marriages involving infants have also occurred, although this happens rarely and usually is only done for specific reasons.
Marriage ceremonies
Marriage customs vary considerably between the lands and major faiths, though all appear to be religious ceremonies between one man and one woman (who should not be more closely related than first cousins). Wedding ceremonies involve the exchange of vows in the presence of particular sacred witnesses, and are followed by a feast, where the bride and groom eat and drink with everyone. Afterwards, the bedding takes place, where the marriage is consummated.
Wedding ceremonies differ between religions. While a priest is involved in ceremonies following the customs of the Faith of the Seven, Lord of Light, and likely the Ghiscari. Ceremonies involving the Faith, the Lord of Light, and the old gods involve the exchange of a "maiden's cloak" and a "bride's cloak"
Wedding ceremonies are generally followed by a feast, which in turn is followed by the bedding. For highborn weddings done by the Faith of the Seven, it is customary to present a wedding pie during the feast, filled with living birds. Dothraki wedding ceremonies might last the entire day, during which the guests feast, drink, dance, and fight. Towards the end, the bride is presented with her bride gifts, after which the marriage will be consummated.
First night
Lords in Westeros once had the right to the first night, the custom of bedding newly-wed women before their husbands. Queen Alysanne convinced King Jaehaerys I to abolish it, but it is still practiced illegally in some parts of the north.
Polygamy
While most marriages are between only one man and one woman, polygamous marriages do occur in the known world. Before the Andal invasion, kings from the Kingdom of the Reach and the Kingdom of the Storm practiced polygamy, as did the dragonlords and sorcerer princes in Valyria, albeit rarely. Polygamy is currently still practiced by some Dothraki Khal's. The "ancient ways" of the Dothraki stated that a Khal might share his Khaleesi with his bloodriders, a custom still practiced in some khalasars today.
Followers of the Drowned God are allowed to take multiple "salt wives" in addition to their "rock wife". Although only the children fathered upon the latter are considered trueborn, any children fathered on salt wives still hold more rights than a man's bastards.