This article contains spoilers. Read at your own risk!
It might spoil your gaming experience when first playing the related games.
The Half-Life series canon has never been officially defined by Valve, and probably never will. Series' writer Marc Laidlaw stated that they do not "get involved in issues of canonicity," that "canon itself is non-canon," and that there is "no official stance," "just the games" as they are. "Canon itself is non-canon" emphasizes the fact that a few to no plot points are set in stone and that they can change anything during the development of further games, the aim being to have a good game before having a good story.
Valve also does not get involved in timeline issues. A complete official timeline of the Half-Life series has never been made and probably never will, since it could probably make the writers contradict themselves and limit their creativity for possible subsequent games. Several retcons have been made and others will likely be made in future games, confirming the "canon itself is non-canon" quote, meaning that any game can have its facts changed in a future release. In that case, if information contained in a new source contradicts facts laid out in an older source, the new source always prevails and overwrites any contradicting data.
Given this lack of reference and stance from Valve, the official source, the wiki had to define the canon itself to avoid confusion, and provide content as consistent as possible to what is set in the final, "real" Half-Life storyline, and what is not. These choices have been made as logically as possible and mirror the general consensus often viewed among fans.
The only requirement for a source to be canon is that it must be official, meaning it has to come directly from Valve, or, if not, be endorsed by Valve.
These endorsed sources are the Gearbox expansions, although their canonicity has been questioned for years, and the Prima Guides, although they sometimes contain inaccuracies and obsolete information, since they are always completed before the game's release. They are considered canon unless they contradict the certified canon material.
The cut material is endorsed by or directly comes from Valve, but is logically deemed non-canon by default. However, some cut content could be deemed canon if it does not contradict the canon material. For example, the Headcrab Shell launcher or the seagulls eating the leeches featured in Lost Coast is likely canon, as it is reflected in the canon games.
Sometimes external sources, such as interviews of Valve employees, provide additional in-universe information. They are included in the wiki as canon as long as they do not contradict the previously established canon.
What follows is listed all the official material related to the Half-Life universe, with their canonicity level. Please note that games series from Valve such as the Counter-Strike, Team Fortress, Day of Defeat or Left 4 Dead series are obviously non-canon, being not set in the Half-Life universe.
Certified canon material
- Half-Life / Half-Life: Source (Features several minor retcons)
- Half-Life 2
- Half-Life 2: Episode One
- Half-Life 2: Episode Two
- The Portal ARG (Not in its entirety)
- The PotatoFoolsDay ARG (Not in its entirety)
- Portal 2: Lab Rat
- Portal 2
- Marc Laidlaw Vault on ValveTime.net (Although unofficial, it gathers e-mails from series' writer Marc Laidlaw, some revealing canonical information)
"Canon unless stated otherwise" material
The Gearbox expansions
The official guides
- Half-Life Prima Guide
- Half-Life: Opposing Force Prima Guide
- Half-Life 2 Prima Guide
- Half-Life 2: Episode One Prima Guide
- The Orange Box Prima Guide
- Portal Prima Guide
- Portal 2: The Official Guide
- Codename: Gordon
- Deathmatch Classic
- Half-Life Deathmatch: Source
- Half-Life: Day One
- Half-Life 2: Deathmatch
- Half-Life 2: Survivor
- Portal: Still Alive
- Sixense DLC for Portal 2
- The Lab
- Anything related to the Half-Life, Half-Life 2 Betas and early versions of the other games that did not make it into the final versions.
- Get Your Free TVs!
- Half-Life: Uplink
- Half-Life 2: Lost Coast
Even if they always contain a small amount of canonical information, most of what is found in these sources pertains to the game's development, and thus covers material that was altered or deleted, making them non-canon, though suitable for discussion regarding cut or altered content.
- Canon on Wikipedia
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