Torchwood is a British television science fiction and crime drama created by Russell T. Davies and starring John Barrowman and Eve Myles. It deals with the machinations and activities of the fictional Torchwood Institute. An initial 13-part series was commissioned by the BBC as a spin-off from the long-running science fiction series Doctor Who; in December 2006, it was renewed for a second series.

An in-house BBC Wales production for digital television station BBC Three, it was the first television spin-off from Doctor Who since the undeveloped K-9 and Company series, of which only a 1981 pilot was made. The spin-off The Sarah Jane Adventures is currently airing on BBC Television, and a further spin-off series K-9 Adventures is in development.

However, Torchwood was the first to be commissioned for a full series. The Canadian network CBC is co-producer of the series, with exclusive rights to broadcast the North American premiere of the show. BBC Wales Head of Drama Julie Gardner serves as executive producer alongside Davies.

The title "Torchwood" is an anagram of "Doctor Who". The name was used as the "codename" for the new series of Who while filming its first few episodes and on the 'rushes' tapes to ensure they were not intercepted. Davies connected the name of Torchwood to an idea for a modern British telefantasy programme in the style of American dramas like Buffy the Vampire Slayer and Angel that he had been developing before he began work on Doctor Who. The name was subsequently used in the series, leading to this spin-off.

The first two episodes of Torchwood premiered on October 22, 2006 at 9 p.m. on BBC Three and BBC HD with all subsequent episodes shown at 10 p.m. every Sunday evening. Each episode was repeated on BBC Two every Wednesday at 9 p.m. The second series will premiere exclusively on BBC Two next autumn. Series One will be broadcast on the ABC in Australia, on TV2 in New Zealand, and on Cuatro TV in Spain in 2007.

The programme began filming on May 1, 2006. Speaking at the London Film and Comic Con on 2 July 2006, Barrowman said that he would finish filming Torchwood in October, "just as it's going on air" after which he has been contracted to appear in the third series of Doctor Who, once again as Harkness. Jack will appear, in Doctor Who series 3 in an episode titled Utopia, having left on the TARDIS in End of Days.

Torchwood is filmed and set in Cardiff. Russell T. Davies told the South Wales Echo, "With Doctor Who we often had to pretend that bits of Cardiff were London, or Utah, or the planet Zog. Whereas this series is going to be honest-to-God Cardiff. We will happily walk past the Millennium Centre and say, 'Look, there's the Millennium Centre.' " The makers of Torchwood deliberately portray Cardiff as a modern urban centre, contrasting with past stereotypical portrayals of Wales. "There's not a male voice choir ... or a miner in sight," said BBC Wales Controller Menna Richards. Conservative MP Michael Gove described the debut of Torchwood as the moment confirming "Wales’s move from overlooked Celtic cousin to underwired erotic coquette."

The team's headquarters, referred to in Doctor Who Confidential as the Hub, is beneath Roald Dahl Plass in Cardiff Bay — formerly known as the Oval Basin. This is where the TARDIS landed in the Doctor Who episode Boom Town and is the location of the spacetime Rift first seen in The Unquiet Dead; this link is alluded to in the first episode. Because the TARDIS landed there the square has picked up chameleon circuit cloaking rendering it invisible. The Hub itself is around 3 storeys high, with a large column running through the middle that is an extension of the fountain above.