Upon a ruler's death his titles will be distributed to other characters based upon what succession law they use. This is not necessarily the same for each title; multiple titles can follow different succession laws. However, it should be noted that only the succession laws of titles on the highest tier you hold matter; everything below that will be given out together with the title it is bound to.
 Succession Law
There are several different succession laws in the game, each with different requirements and effects. There is no 'best' succession law, which you'll want depends upon your goals for the campaign. Below is a list of all succession laws. Do note that Muslims can only use Agnatic Open (Turkish) succession, while unreformed Pagans can only use Gavelkind. Succession laws consist of a type of succession, and a gender law.
Succession laws can only be changed by a ruler who is at peace and has ruled for 10 years. A given ruler may only change one succession law for each held kingdom or empire. In addition, either all direct vassals (for counts and dukes) or all direct vassals of count rank or higher (for kings and emperors) must have a positive opinion of the ruler. Since this only applies to direct vassals, a particularly troublesome vassal can sometimes be dealt with by transferring that vassal to a higher-ranked subordinate.
Also note that every single one of your direct vassals and direct family members will have a large penalty or moderate bonus temporary but long-lasting opinion modifier as a reaction to a succession change, whether it be gender or succession method itself. This appears to be hardcoded (unmoddable) and largely random as for example female family members will be outraged at a change to true cognatic even if it makes them the new heir, and includes baron-level vassals who in theory should have little if any opinion about it.
At duchy level and lower, a single succession law covers all of a character's titles. However if a character holds multiple kindom or empire titles these will each have their own succession law, which may lead to different heirs for each kingdom title.
Some characters can never inherit any titles. Bastards cannot inherit unless they have been legitimized, nor can characters who have been made bishops, nor can eunuchs. All other characters can inherit if they're eligible under the title's succession laws.
 Succession Types
|Gavelkind||Titles distributed between all children. +30% demesne limit||-10 oldest child, +30 other children, +10 dynasty, +5 vassals||N/A|
|Seniority||Oldest dynasty member inherits||-10 vassals, -30 oldest child, -20 other children, +10 dynasty||Medium Crown Authority, or Patrician family.|
|Primogeniture||Oldest child inherits||+20 oldest child, -20 other children, -5 dynasty||High Crown Authority|
|Feudal Elective||Every major ruler in the realm votes for the heir||-30 oldest child, -10 other children, -5 dynasty, +20 vassals||N/A|
|Open||Child (or grandchild) with best titles inherits||-10 oldest child||Muslim|
|Open Elective||A generated character inherits||N/A||Burgher or clergy|
|Patrician Elective||Only used by merchant republics, person with most 'respect' is elected||N/A||Is republic|
|Catholic Bishopric||A generated character inherits, but can be overridden by Investiture||N/A||Catholic Bishopric|
|Ultimogeniture||Youngest child inherits||+20 youngest child, -30 oldest child, -20 other children, -5 dynasty||Low Crown Authority, Not Pagan or Muslim|
|Tanistry||Like Feudal Elective but all titleholders in realm can vote, and they must select a dynasty member||-40 oldest child, -20 other children, +10 dynasty, +5 vassals||Low Crown Authority, Celtic culture or Human Player|
 Succession Type Notes
If the ruler holds multiple duchies (and no kingdom), or multiple counties (and no duchy), Gavelkind will result in each sibling becoming in charge of an independent realm after partition. When this occurs, all children will receive strong claims on their sibling's titles, allowing for a potential quick but bloody reunion. However, when the realm is not split up, the eldest child does not receive claims on the titles handed to his (now vassal) siblings.
Gavelkind also prevents the prestige penalty normally incurred for having unlanded adult sons.
Valid electors are all holders of de jure vassal titles one tier lower than the elected title, while in titular realms, all vassal rulers of the appropriate rank may vote. Empires are an exception: both dukes and kings may vote. Each ruler gets a single vote regardless of how many electoral titles he holds. The current ruler always gets a vote as well even if he does not hold any elector titles.
Eligible candidates are:
- All (gender-law allowed) dynastic children, grandchildren, siblings, nephews and nieces of the current title holder. If any of these don't belong to your dynasty, they won't be eligible, unless they are landed inside your realm,
- All current electors (including dejure and foreign ones),
- Any claim holder on that specific title.
Female children may be nominated under Agnatic-Cognatic law even if they have brothers, so there is no effective difference between Agnatic-Cognative Elective and Absolute Cognative Elective for succession purposes (however Absolute Cognative will allow granting landed titles to females that is prevented by other succession rules).
Under Feudal Elective, your choice of heir will get a +50 opinion bonus.
Merchant Republics always use Patrician Elective. The candidates are the heir of the current doge and the leaders of the other four patrician families. Each candidate has a Respect value, equal to the square of their age, plus their prestige value, plus five times their money invested in a campaign fund. Generally, the candidate with the most Prestige wins, but there is a chance that the second-place candidate wins instead if the Respect values are fairly close. Children cannot be elected.
The patrician families always use Agnatic Seniority. The ruler may choose to designate an heir using an honorary title, which overrides the usual rules of seniority.
Both of these rules take precedence over other restrictions on succession - so Muslim and Pagan republics work in the same way as Christian ones.
Succession in the Byzantine Empire is further influenced by the Born in the Purple trait and the Despot Honorary Title. Characters who have either of these attributes are considered higher in the succession order than those without.
 Gender Laws
|Agnatic||Only males can inherit||-10 female dynasty members||N/A|
|Agnatic-Cognatic||Women can only inherit if there are no eligible males||N/A||Not Muslim or Tengri|
|Absolute Cognatic||Women inherit on equal terms with men||-10 male dynasty members||Basque culture or Cathar religion|
|Enatic-Cognatic||Males can only inherit if there are no eligible women||N/A||Unavailable by default, can be modded in, but basic code support exists|
|Enatic||Only women can inherit||N/A||Unavailable by default, can be modded in, but basic code support exists|