Talent

Talents are special abilities that can be chosen to augment your character. Talents may be passive bonuses or active abilities. Each class has its own selection, with 21 talents split over 7 tiers. Talents are limited by level, with a new tier becoming available each 5-10 levels for all classes. Talents are class-specific, and a majority of choices depend on specialization. Talents offer a further level of customization beyond class and specialization selection, and can be changed very easily and cheaply.

Full listings of the talents available to each class can be found on that class's abilities page, e.g.: Priest abilities.

Talents can be swapped at any time while in a rested area, or for a short time after queuing into an instanced dungeon, raid, or PvP content. Tome of the Clear Mind or Tome of the Tranquil Mind is required in other situations; Codex of the Clear Mind or Codex of the Tranquil Mind can be used in group settings.

Gaining talents
Talents are split over 6 tiers, with 3 talents on each. Each tier is unlocked when the character reaches the appropriate level. For all classes, a new tier becomes available every 5-10 levels.
 * Tier 1: level 15
 * Tier 2: level 25
 * Tier 3: level 30
 * Tier 4: level 35
 * Tier 5: level 40
 * Tier 6: level 45
 * Tier 7: level 50

Tips

 * Many talent tiers offer choices between benefits to different aspects of your character, or different combat roles. Some are also better oriented for PvP or PvE.
 * If you intend to participate in end-game PvE raid content, it is recommended to choose talents with the boss encounter in mind. For example, a talent that improves damage or survivability against the boss might be preferred over a talent that only improves damage or survivability against trash mobs. The raid will undoubtedly find the boss encounter more difficult, and preparing for it will aid in surpassing the challenge.
 * While leveling, feel free to experiment with talents and choose that are the most handy or useful for you. Talent choices will likely differ at max level anyway, and in the mean time convenience and enjoyment is usually more important. In addition, leveling frequently involves participation in multiple types of play (questing, instances, PvP) and so it is unlikely that a single talent build will be ideal for all play, and usually uneconomical to reset them for each situation. However, be aware that when playing in groups, your talent choices may impact other players; if anticipating a tough encounter, you may wish to re-customize your choices accordingly.

History
Talents have gone through some very substantial changes over the years. The prime form of character augmentation and customisation in World of Warcraft, talents were the predecessors of specializations, predating the introduction of fixed specializations by many years. Originally a complex and intricate system of possible combinations, since Wrath of the Lich King talents have been reduced and simplified, with many of their earlier functions being split off into other mechanisms. The original means of customising your character's abilities and combat role, Cataclysm saw the creation of specific specializations, making the selection of a player's talents more helpful than critical, while Mists of Pandaria saw them converted to a far simpler system, with choice no longer determined by specialization or previous selections. While the current system features a fraction of the number of talents previously known, a large amount of talents have been converted into specialization-specific or class-wide abilities, with many key abilities having started life in the higher tiers of a class's pre-historic talent trees.

Pet talent points
Prior to Patch 5.0.4, hunter pets enjoyed their own talent system, featuring trees in which hunters could spend each pet's talent points. The pet talent system was removed with Mists of Pandaria, with many talents removed, and the rest converted into specialization-specific pet abilities.

Patch changes