Doctor Who universe

The Doctor Who universe, or Whoniverse, is a term used by fans, and increasingly the mainstream press, to describe the shared fictional universe in which the stories of Doctor Who, K-9 and Company, Torchwood, The Sarah Jane Adventures and K9 take place.

Semantic origins
The term "Whoniverse" dates at least as far back as Peter Haining's 1983 book, Doctor Who: A Celebration. At that time, the Whoniverse had a very broad meaning, which included not just the setting of Doctor Who stories, but everything about the series, including behind-the-scenes information and fandom itself.

Recent developments
"Whoniverse" gradually became a more specific term, at first used as a way to emphasize that Doctor Who stories told in other media were part of the same universe as those told on television and that Doctor Who and its spin-off series take place in the same universe. Prior to Torchwood and later The Sarah Jane Adventures, Doctor Who had not had a successful spin-off series. Series 1 of Doctor Who also included references to the planet Lucifer, kronkburgers and Justicia, hinting that non-televised Doctor Who stories might take place in the "official" Doctor Who Universe.

Martha Jones's employment by UNIT first got a mention in the Torchwood episode Reset, in which she appeared, and The Sontaran Stratagem/The Poison Sky had a semi-sequel in the form of the The Sarah Jane Adventures story The Last Sontaran. The Stolen Earth/Journey's End brought together cast members of three series. A number of more casual mentions have also taken place, such as Sarah Jane suggesting "Harry" and "Alistair" as possible names for Luke in Invasion of the Bane. Likewise, Sarah's description of the origins of her coulrophobia in SJA: The Day of the Clown returns the viewer to the setting of A Girl's Best Friend. While such "crossovers" can be narratively insignificant, they nevertheless reinforce the notion of a single, shared universe.

The production team of the current production Doctor Who, shy away from defining what is or is not canon. Steven Moffat observed at the 2008 Comic Con in San Diego that it is "impossible" for a show about a dimension-hopping time traveller to have a canon. Any disagreements between Doctor Who source material can be quickly rationalized by saying, "The audience just hasn't seen the adventure when the Doctor goes back in time and changes that detail."

Series writer Paul Cornell has stated in his blog that he does not believe that a Doctor Who canon actually exists.

Integrating elements into canon
Fans have tended to not accept older elements, such as material presented in the Doctor Who Annual, the comics published in TV Action into canon. The theatrical films Dr. Who and the Daleks and Daleks - Invasion Earth 2150 AD, which portray a Human "Dr. Who" played by Peter Cushing are generally considered not canon, but a number of attempts have appeared to explain them away. The short story The Five O'Clock Shadow, the universe of the Dalek movies is described to be a sort of fairy tale that the First Doctor tells to Susan. Thus, while the Dalek movies are not set in the Whoniverse, some writers have chosen to consider them loosely canonical.

Likewise, the comic characters of John and Gillian are not generally regarded as inhabitants of the Whoniverse, but they have been made canonical by later writers' efforts to explain them as products of the Land of Fiction or dreams of the Eighth Doctor. (DWM: The Land of Happy Endings)

Other information and trivia

 * The All-New Official Handbook of the Marvel Universe Volume 1, #7 designates the Doctor's universe as Earth-5556.