Canon is "any material that is considered to be "genuine", or can be directly referenced as material produced by the original author or creator of a series". The canon of the Smallville television show is considered source material for this site, the Smallville wiki. This is a partial and emerging list of all material that is considered canon.
Information from every aired episode is considered the primary source of canon for the Smallville wiki. This includes:
- Dialogue: Considered the primary source of information for the site, as it is objective and straightforward.
- On-screen text: Written material that is readable to the viewer, such as computer screenshots, Chloe's toe tag in Bizarro, or Lois's article about Adrian Cross she submitted to the Daily Planet.
- Closed-captioning or subtitles: Occasionally provide information that can be considered canon.
- Deleted and expanded scenes: Scenes included on the DVD box sets. This does not include alternate scenes, which contradict the plotline or are significantly different from the same timeframe on the aired episode.
- Director and actor commentaries: Audio commentaries included on the DVDs.
- Unaired scenes (e.g. the first version of the Pilot episode).
- Chloe Chronicles
- Oliver Queen Chronicles (episodes 1 to 3 only) - Season 6 DVD
- Kara and the Chronicles of Krypton - Season 7 DVD
TV Guide Comic
DC Comics released 12 separate comic books filled with 21 separate comic stories:
Smallville Ledger and Torch articles were published on Warnerbros.com during the first four years of the show:
- Smallville Ledger
- Smallville Torch}
- Lois also published an article for the Metropolis Inquisitor 
There were 18 novels published altogether, with 8 being regular Novels and 10 Young Adult Novels:
Ezra Small Prophesies
A series of prophesies published in Smallville Magazine and online 
- Older internal sites from Warner Brothers, such as LuthorCorp.com or Smallville.com
- Bios for Lex and Lionel
- Chloe's database of meteor freaks
- Chloe's Operating System
- CKU website, including page for Students for Lex Luthor
- Project Mercury blog on AOL 
Smallville: The Visual Guide
- Smallville: The Visual Guide follows Clark Kent's development from a shy farm boy to a super hero on the brink of fulfilling his destiny. The Smallville Visual Guide was produced in collaboration with DC Comics and Warner Bros.
Smallville Companion Guides
- Companion guides to each season, published by the webmaster of Kryptonsite with permission and cooperation of the show's producers
Titan Magazine has published 28 issues of Smallville Magazine, including many short stories featuring characters from Smallville. Creative work from the magazine, such as short stories, comics, and other "in-universe" material, can be considered canon. More expository or editorial articles can be referenced, but it should explicitely stated that they are the opinion of the magazine's writing staff, not necessarily created or by the show producers or writers.
- Please add any short stories to this list.
Occasionally the show releases merchandise and online material to generate promotion for the show:
- Justice & Doom contest prizes such as clues from the "missions" and Veritas Society meeting notes 
- Toyota Yaris gave away copies of the flash drive from Progeny as part of a promotion, containing detailed information on Moira Sullivan.
- The Daily Planet "articles" published on giveaway bags for 2008 ComicsCon visitors.
Sometimes writers or producers will give interviews and offer insight into plotlines or details that were not actually revealed on the show. If editors can find an easily-accessible source to verify such information (like a link), it is appropriate to add it to the wiki. (It is not enough to just say "I read/heard somewhere that Al Gough said...")
Occasionally, two credible sources of canon contradict. In general, if it is a case of the show depicting one idea, while an off-show source, such as a Ledger article, depicts another, then the episode itself takes precedence.
If the contradiction is within the episode itself, the site will defer to the dialogue, simply because that is the easiest medium available to the viewer. For example, in the episode Witness, the Andy Connors character is referenced in the dialogue as one name, but the visible police report gives him another.
Other contradictions are more subtle, such as the pronunciation of the town of Granville. Many viewers hear it pronounced "Grandville" but in this case, on-screen text was used to come to a consensus for the site.
However, most of the time, the wiki will indicate that there is a contradiction of canon so that site visitors can be aware of all relevant sources and come to his or her own conclusion.