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Doctor Who is a British science fiction television programme produced by the BBC. The programme depicts the adventures of a mysterious alien time-traveller known as "the Doctor" who travels in his space and time-ship, the TARDIS, which normally appears from the exterior to be a blue 1950s police box. With his companions, he explores time and space, solving problems, facing monsters and righting wrongs.

The programme originally ran from 1963 to 1989. After an unsuccessful attempt to revive regular production with a backdoor pilot in the form of a 1996 television film, the programme was successfully relaunched in 2005, produced in-house by BBC Wales in Cardiff. Some development money for the new series is contributed by the Canadian Broadcasting Corporation (CBC), which is credited as a co-producer. Doctor Who has also spawned spin-offs in multiple media, including the current television programmes Torchwood and The Sarah Jane Adventures, and a single 1981 pilot episode of "K-9 and Company".

The show's lead character, the Doctor, has been played by ten actors over the history of the show. The transition from one actor to another is written into the plot of the show as regeneration, and the different parts are often treated as distinct characters to the extent that in some time travel plots they encounter one another and work together. The Doctor is currently portrayed by David Tennant. In the programme's most recent series, which ran from 5 April to 5 July 2008, Catherine Tate played the Doctor's companion, reprising her role of Donna Noble from the 2006 Christmas special. A Christmas special, entitled "The Next Doctor", was broadcast in 2008 and will be followed by four more specials in 2009 and early 2010; the next full series, series 5, has been confirmed to air in 2010. Tennant announced at the 2008 National Television Awards that after appearing in the four 2009–2010 Doctor Who specials, he will leave the role. The Eleventh Doctor will be portrayed by Matt Smith.

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