The main concept behind skill balancing is to prevent any set of skills in a build (for example, a healing monk) from becoming overpowered to the point where no other build is used to achieve the purpose of that build, simply because it would not make sense. In PvP, the player community will always go for the most efficient build. As such if one build is proven to be a lot more effective than all other builds, everyone in the community will simply run that build and ignore all others, removing diversity from the game as well as a lot of excitement. In PvE, if a build is far more effective at killing monsters than any other build, everyone will simply play that build to farm those monsters and, again, variety (examples) will be taken out of the game as well as a possible inflation in the game's economy.
An example of this concept is the nerf to the Ritual Lord build for ritualist. The build was so effective at buffing up the defenses of a team that almost no one played anything but Ritual Lord in the ritualist profession especially in PvP where it made little sense since no other build could benefit a team as much as a Ritual Lord could.
Another important concept is to prevent skills from falling out of practical use. If there's a large number of skills in a profession which not many players are trying to use in PvP or PvE, the developers will try and strengthen that line of skills to give it more life and usage.
An example of this concept would be the buff to the Channeling Magic line for the ritualist profession. The line was nearly abandoned in both PvP and PvE partially because of the dominance of Ritual Lords mentioned above, and partially because it could not mete out as much damage as elementalists and necromancers. It's damage has been increased as well as its ability to keep dishing out damage.
 Notable skill balances
- August 25 2005: The first skill balance, dealing with Chain Lightning spike teams, spirit spam Rangers, and Protective Bond Underworld solo Monks.
- September 29 2005: Dealing with Ether Renewal Elementalist smiters and some aspects of Ranger spike.
- April 26 2006: Dealing with balancing existing skills with new Guild Wars Factions skills and professions.
- July 13 2006: Dealing with Air of Enchantment Smiters, Fast Casting Mesmer-Elementalist spikes, and Feast of Corruption spikes.
- October 25 2006: Dealing with balancing existing skills with new Guild Wars Nightfall skills and professions.
- January 19 2007: Major balance dealing with rebalancing new Guild Wars Nightfall skills and professions. Also introduced rit spiking to the meta.
- February 1 2007: Second major balance dealing with rebalancing new Guild Wars Nightfall skills and professions.
- April 10 2007: Rebalancing some necromancer skill to work better with the new Soul Reaping mechanics.
- June 15 2007: Various skill changes focusing in GvG play.
- August 9 2007: Major balance promoting more variety in builds and a preemptive balance for the Eye of the North expansion.
- May 22 2008: Introduced a new system to split certain skills into separate PvE and PvP versions.
- December 11 2008: Major functionality changes of various elite skills.
- June 18 2009: Split of spirits and chants to PvE and PvP versions. PvE versions buffed to increase usage.
- January 28 2010: Rework of several PvP skills to make blood spike less effective.
- February 25 2010: Rework of skills to limit overpowered farming builds, and buffed less popular builds for PvE.