This wiki's canon policy is pretty simple: Doctor Who and its related programmes have no canon. Therefore, we allow articles about most officially licensed stories. However, we do define what stories serve as valid sources to write our in-universe articles.
Background
The idea of a fictional series having a "canon" was first used by fans of Sir Arthur Conan Doyle's Sherlock Holmes series, who for nearly a century have played what they call the "Great Game": pretending that Holmes' adventures were actual events, recorded by Dr. Watson, with Conan Doyle acting as their literary agent. Sherlockians playing the "Great Game" use evidence from Conan Doyle's stories to deduce unrecorded details about Holmes' and Watson's lives. To do this, they needed rules for the game, and one of those rules was that only stories by Conan Doyle "count". Sherlock Holmes pastiches and tributes by other authors are legion, so the Sherlockians took a page from Biblical criticism and declared that the 56 stories and four novels by Conan Doyle constituted the Sherlock Holmes canon.
On this wiki, we're doing something similar: we're pretending that all Doctor Who stories took place, and creating a hyperlinked encyclopedia of the universe that's constructed. Just like the Sherlockians playing the Great Game, we need to establish rules; but since Doctor Who is so vast, with stories in so many different media, and since it doesn't have a single author, the business of determining what "counts" is much more complicated.
Doctor Who and canon
If you're new to Doctor Who you may be unaware the Doctor Who universe or DWU — is much more amorphous than the typical fictional universe. The primary copyright holders to the DWU, the British Broadcasting Corporation, have deliberately refused to say which stories "count" and which don't. In general they've been wholly silent on defining a canon of any kind.
In fact, the DWU isn't even wholly owned by one entity. For over 35 years, Star Wars was ultimately owned by one person, George Lucas. Star Trek is owned by CBS. But, due to oddities in British television practices, the DWU is primarily owned by the BBC, but individual elements within the DWU, like the Daleks, the Autons and even individual characters like Nyssa and the Brigadier, may be owned by individual authors.
This highly complex legal situation makes it impossible for the BBC to define a canon, because they simply don't have the right to wholly define it. Daleks can appear without any other DWU elements. John Benton has been in a story without the Doctor. And K9 can get his own television series in Australia regardless of the BBC's wishes.
In other words, a story set in the Star Wars universe had to receive the blessing of George Lucas. A story set in the DWU doesn't necessarily require the assent of the BBC. Since canons are definitionally created by a single authority, the DWU cannot ever have a canon.
But still the new stories come. Unlike Holmesian literature, over a hundred new DWU stories are published annually. So our version of "the Great Game" is less like a cozy bit of drawing room speculation over a brandy and a fine cigar — and much more like being a quality control checker on an assembly line. The only thing we try to do is develop a series of litmus tests that will allow us to quickly spot the defective merchandise as it hurtles towards us down that relentless conveyor belt.
Policy in detail
The legal inability of the BBC to define canon doesn't mean that "anything goes" on this wiki. A lack of canon has three separate impacts upon our database, resulting in three major types of article: "real world", "in-universe" and "non-DWU".
- Real world articles are those that are written about stories, as well as those on behind-the-scenes people and concepts. Because we don't believe there is such a thing as a "canon" for Doctor Who, we allow just about everything that was released under license from the appropriate copyright holder(s) to have a "real world" page here. So there are pages here for even very marginal pieces of Doctor Who like A Fix with Sontarans, Dr. Who and the Daleks and Exile.
- In-universe articles are those written about the narrative elements of the DWU — articles like Amy Pond, ambulance and Andromedan. The only valid sources for these articles are stories. Thus we need to know which stories "count" and which don't. If we didn't attempt a little bit of definition, our biography of the Doctor would have to include "the time he spent on Earth when he was a human called Dr. Who" or "the incident in which he regenerated into his thirteenth body that looked an awful lot like Joanna Lumley", "the one time he sounded an awful lot like Nick Briggs, "the other time he sounded an awful lot like Nick Briggs", and so forth.
- Non-DWU articles are those which flow from officially licensed stories which are not considered valid sources. For instance, we do allow articles on the Peter Cushing Doctor and the Shalka Doctor, even though the stories from which they come are not valid sources. However, such pages must clearly be labelled with {{invalid}} and these articles shouldn't be linked or referenced in the in-universe portions of in-universe articles. Such pages must also be kept out of in-universe categories — The Master (The Curse of Fatal Death) must never be placed in category:Individual Time Lords.
Again, this wiki makes absolutely no attempt to define the "Doctor Who canon". If you want to believe that the parody comic strip Doctor Who? is canon, feel free. If you think that Dimensions in Time reveals a genuine adventure of the Sixth Doctor and the Brigadier, by all means revel in that belief. You're completely free to write "real world" articles about anything that's properly licensed from the appropriate copyright holder(s). But the fact that there's a real world article about a story doesn't mean that you can use that story to write an in-universe article. Only stories on the valid sources list can be used to write in-universe articles.