Marriage is the religious, political, and personal union of two characters in 
Crusader Kings II.
Effects of marriage
When two characters are allowed by their lieges to get married, the union gives the following effects:
- The wife joins her husband's court in a standard (patrilineal) marriage. But in a
matrilineal wedding, the husband joins her court instead. Therefore, the player should be careful while arranging spouses for their courtiers or relatives - In a patrilineal marriage, descendants belong to the father's dynasty; Otherwise, the offspring belongs to the mother's dynasty. If the player ends up with no characters belonging to the current dynasty they're playing as, it is game over
- The player character can produce legitimate children to get an Heir(ess) and expand the player's dynasty
- The character gains bonus prestige if their spouse's dynasty is more distinguished
- The character gains or loses prestige depending on their spouse's rank (+100 / -100 per difference of rank; no prestige adjustments if both bride and groom are Muslims)
- Half of spouse's attributes are added to the ruler's state attributes
- It is worth noting that half of spouse's
stewardship is taken into account when calculating demesne limit.
- It is worth noting that half of spouse's
- The wife (or mother) of a ruler may occupy the spymaster position on the council (although doing so may lower state intrigue, due to how state attributes are calculated). Afterwards, the liege's wife becomes qualified to occupy other positions if the realm improves the Status of Women law (requires the
Conclave DLC).
Union types
There are 6 types of unions:
| Union | Requirement | Effect | |
|---|---|---|---|
 |
(Patrilineal) Marriage | Bride & groom ages >= 16 | Children born from the union will belong to the father's dynasty |
|
Matrilineal Marriage | Bride & groom ages >= 16 | Children born from the union will belong to the mother's dynasty |
 |
Concubinage | Bride & groom ages >= 16 | Extra consorts of men who are Pagan, Zoroastrian, Tribal or follow the Eastern religions |
|
Consortage | Bride & groom ages >= 16 | Extra consorts of women who are African pagan, Bön pagan or follows reformed pagan religion with Enatic Clans or Equality doctrine. |
 |
Betrothal | Either bride or groom age < 16 | Commitment to a patrilineal marriage once both are over 16 |
 |
Matrilineal Betrothal | Either bride or groom age < 16 | Commitment to a matrilineal marriage once both are over 16 |
Matrilineal marriage
A matrilineal marriage helps to secure a dynasty where most heirs are female, by making the children born from a marriage part of the mother's dynasty, and prevents game over if the succession gender law is strictly agnatic.
Rulers will usually not accept a matrilineal marriage with a son that is in the direct line of succession or has titles/claims. So the potential benefits are reduced compared to a standard patrilineal marriage.
Matrilineal marriages are not available to merchant republics, and require high status for women if to be available for Muslims. It should be noted that for a matrilineal marriage to be possible between the player's court and another character's court, both characters must have a gender succession law which allows matrilineal marriage. This can be bypassed by using a favor to invite the marriage target to the player character's court (requires the Conclave DLC). Similarly, characters who have claims can be invited to the player character's court by using a favor, before carrying out the matrilineal marriage (as long as they are not a councilor or close relative of their current liege).
Before 
Holy Fury, matrilineal marriages are always monogamous; a woman can never take multiple husbands or have male concubines. However, up to 4 Muslim women may be matrilineally married to the same Muslim man. With Holy Fury, female reformed pagans whose faith has the Enatic Clans or Equality doctrine can take up to 3 consorts.
Betrothal
A betrothal is a commitment to a future marriage once both parties are over 16. To follow through on a betrothal, the player must click the alert, or re-enable it if they had disabled it previously.
Betrothals prevent the character from going off and marrying someone else automatically. Rulers cannot declare war on other rulers if close relatives are betrothed.
AI rulers will only arrange betrothals among themselves if their children are over 12. To be certain that the player character will secure a betrothal, the player should suggest it before the AI's children turn 12.
Remarrying
A mother will keep very good relations with her own children, but not with the children from her husband's previous marriages.
As such, when the character is remarrying and having more children, a new wife might try assassinating children from his previous marriage to pave the way for her own heirs.
Potential spouses
There are several criteria to consider when picking spouses:
Fertility and Health
One of the goals of marriage being to produce a male heir, unless the status of women is high enough, fertility and health are fairly important factors when choosing a future spouse:
- Some traits increase fertility:
(+10%), 
(+20%), 
(+20%), high end stewardship and diplomacy education traits - Women become completely infertile at 45 years-old
trait makes it impossible (-5000% fertility penalty) for a male ruler to marry or produce children
trait makes it very improbable (-1000% fertility penalty) to get a wife 
- Some traits reduce fertility:
(-5%), 
(-15%), 
(-15%), 
(-30%), high end learning education traits, and diseases. It should be noted that some of these traits also reduce health, which may lead to early deaths and remarriage, which then leads to other issues, as mentioned above.
Congenital traits
- 主条目：Breeding
Genetic Traits are those that can pass down to children.
The good ones (in ascending bonuses) are 
, , 
, and 
.
Attributes
- 主条目：Attributes
Marrying a spouse with high stats can make a big difference in how well a realm is managed:
- Half of the spouse's attributes are added to state attributes. Note: for Muslim rulers, only the primary spouse's attributes count
- The spouse's
stewardship attribute contributes toward the demesne limit: +1 at stewardship 7, +2 at stewardship 14, and +3 at stewardship 20 - The character's wife can be appointed as spymaster, but her skill will only contribute once to state attributes (not 1½ times). Muslim rulers' secondary wives are exempt from this (since they don't provide stats as wives)
- If the spouse has higher numbers in any attribute, some events will allow the player character to ask for her help. This usually gives a positive temporary modifier to some aspect of the realm, and a 20% chance of getting +1 point in that attribute. However, there's also a 80% chance to get the
trait.
Alliances
- 主条目：Alliances
Players are automatically engaged in a non-aggression pact to another ruler if close relatives are involved in marriage. An alliance can be arranged with someone the player character already has a non-aggression pact with. As long as a member of the player's immediate family (children, grandchildren, siblings, grandparents, or parents) is married to a member of their immediate dynasty, the alliance or non-aggression pact persists until broken upon death. Close relatives can ask for non-aggression pacts to be formed.
Vassals engaged in non-aggression pacts to their liege may not join any factions against them, but also ensures protection from the liege in return. Thus, a marriage with a vassal is a good way to placate them, but also incurs a risk as they may get a claim on the player character's primary title.
Titles and claims
Spouses with claims (or who will receive claims upon the death of their parents) will pass their claims on to their children. This is the cleanest way to get claims on new land. A good strategy is to marry characters with titles as, depending on laws of the realm, the offspring may inherit them and unite both realms upon succession. A female ruler who marries a male of the player's dynasty non-matrilineally will produce heirs of his dynasty, consolidating titles and spreading the influence of the player's family. Thus, it opens up more alliance options to be exploited.
Prestige effects
Each spouse gains or loses prestige based on rank difference and the other's dynastic prestige. Prestige effects are pivotal in AI consideration of marriage proposals.
A character's marriage rank is the highest rank title held by {self, parents, grandparents, siblings, children?}, living or dead. However, titles held by rulers with any republic-type government do not count toward marriage rank.
The lower rank character gains +100 prestige per rank difference, while the higher rank character loses -100 prestige per rank difference beyond the first. E.g., if a count marries a king's daughter (two ranks higher), he gains +200 prestige and she ends up with -100 prestige. The effect of dynastic prestige, however, is positive for both characters.
Muslims do not have prestige effects from marriage. This reflects their polygamy and strictly agnatic open succession. However, this happens only when both bride and groom are Muslims.
Caste
- 主条目：Caste
A Hindu-only consideration. There are 3 castes: 
are temple rulers, 
rule over castle holdings and 
are city rulers.
Both characters are highly encouraged to be of the same caste in order to get wed. A marriage across castes will result in opinion penalties from other Hindus, as well as their children will recieve the lower caste at birth.
Religion
With Holy Fury, reformed pagans whose faith has the Dogmatic nature cannot have interfaith marriages.
Consanguinity
Consanguinity can be a problem, as the interface doesn't inform the player about close relatives who are not dynastic. Marriages among relatives may yield children with the debilitating trait. Generally, if the bride and groom do not share any grandparents, the marriage can be considered to be relatively safe.
Bloodline
- 主条目：Bloodline
Introduced with Holy Fury, 
Bloodlines can be a large consideration for spousal selection. Although difficult to do, given that most historical bloodlines and many created bloodlines will be patrilineal in nature, breeding bloodlines into one's dynasty and succession allows for your decedents to take advantage of their modifiers or granted abilities.
Bloodline inheritance, although similar to both dynasty and congenital inheritance, is distinct as it is connected to perceived descent. This means that considerations for inheritance will need to be different, depending on the nature of the bloodline.
Arranging marriages
Clicking the 
Arrange marriage button below a portrait opens a list of suggested spouses, ordered by a combination of title rank and marriage rank. You can also arrange marriages from the diplomacy screen of one of the characters, or from the diplomacy screen of a courtier's liege.
Many factors affect AI acceptance of marriage proposals. If a liege won't accept a marriage proposal, try a bribe, or consider inviting the character to your court to gain full control over who they marry.
Lovers
Married lovers have increased fertility. Unmarried lovers have much lower fertility.
A child born to unmarried lovers will be a 
, unless the woman is married and fools her husband into believing he is the child's father. Bastards can be legitimized into the dynasty of either parent. Bastards who remain illegitimate cannot inherit and will create a new (and unrelated) dynasty if they have any children of their own.
Summary
Through well thought-out marriages, the player can forge powerful alliances, expand their dynasty, and ensure good heirs. Bad marriages, on the other hand, could have the player character ends up dead or with an heir.
- Avoid marriage with close family (at least no common grandparents between bride and groom), and marry characters with high fertility, titles or positive congenital traits
- Try to preserve the dynasty: Marry sons patrilineally and daughters matrilineally, if needed
- Remember that matrilineal marriages are unavailable to merchant republics and generally not for Muslims with low status for women. Also, if the player character is a female ruler, matrilineal marriage is the option to preserve the player's dynasty (apart from having legitimized bastards).