Unlock

Overview
In Guild Wars, "to unlock something" generally means to make it available for your PvP characters. Unlocked skills can also be equipped by Heroes, and unlocked non-Elite skills will be available for purchase from skill trainers of their chapter for future PvE characters. Currently, you can unlock skills, runes, weapon upgrades, and Heroes. You can unlock via either PvE or PvP.

Unlock via PvE

 * Learning a skill (regardless of whether it's from a quest, skill trainer or captured from a Boss) will unlock the skill. Even skills learned temporarily before acquiring a secondary profession are unlocked. In Guild Wars Nightfall, whenever a Hero is recruited, every skill on that hero's default skillbar is also unlocked.
 * Identifying a weapon upgrade or rune from loot will unlock it.
 * Visiting a Priest of Balthazar by traveling to the Great Temple of Balthazar and unlocking a skill with a PvE character does not make that skill available to the PvE character.
 * Having a Hero join your party for the first time unlocks him/her for PvP Hero Battles.
 * Notes:
 * You do not unlock things that you buy, only things that you identify by use of an Identification Kit. This means that if you buy a weapon upgrade from a fellow gamer, you will not unlock it, unless it is still "unidentified".
 * Buying a rune from a Rune Trader will not unlock it. Runes can only be unlocked by using an Identification Kit on salvage items such as Ettin's Pauldrons or Seeker's Vests. If you salvage the salvage item before identifying it, you will receive an unidentified rune, which can then be identified to unlock the rune.
 * When you identify a weapon upgrade with a higher bonus than you have previously unlocked, you unlock that upgrade with the newer, higher bonus. For example, let's say you have never identified any swords before and you identify a sword that turns out to be a "Fiery Fellblade of Enchanting". This will unlock "Fiery Hilt" and "Sword Pommel of Enchanting" with a particular bonus (10...20%) to enchantment duration. If it turns out to be 12%, then your PvP characters will have that pommel available to them with the same 12% bonus. If you later identify a sword with a higher bonus, you unlock the higher bonus.
 * "Green" Weapons are identified when they drop, therefore they cannot be used to unlock weapon upgrades.
 * Celestial skills and holiday event skills cannot be unlocked.

Unlock via PvP
You can trade your Faction points at a Priest of Balthazar to unlock skills, runes and weapon upgrades.

Skills cost 1000 faction points to unlock a regular skill and 3000 faction points to unlock an elite skill.

Runes are unlocked in this order: minor runes cost 1000 faction points, then major runes cost 1500 faction points, and finally, superior runes cost 2000 faction points.

Weapon upgrades that come with varying numbers (such as Sundering or +1 to skill) follow a certain sequence for unlocking. If the upgrade has never been unlocked on your account, the unlocked upgrade will have the minimum possible value. If the upgrade has been unlocked at least once in PvE or PvP, the second unlock will have the highest numbers possible. Weapon upgrades cost 1000 faction points to upgrade at each stage.

Heroes can be unlocked for 3000 to 6000 Faction points.

Unlock via other methods
It is currently possible to unlock all of the skills in a particular campaign by purchasing the Skill Unlock Packs of that campaign via the Guild Wars In-Game Store.