"The Unquiet Dead" is the third episode of the first series of the British science-fiction television programme Doctor Who, first broadcast on 9 April 2005 on BBC One. It was written by Mark Gatiss and directed by Euros Lyn.

In the episode, the alien time traveller the Ninth Doctor (Christopher Eccleston) and his companion Rose Tyler (Billie Piper) travel to Victorian Cardiff on Christmas Eve, 1869 where there have been sightings of strange gas-like creatures. The Doctor and Rose team up with Charles Dickens (Simon Callow) to investigate Mr Sneed (Alan David), a man who runs a funeral parlour where it seems that corpses have come to life. It is revealed that the gaseous Gelth (voiced by Zoe Thorne) have entered Cardiff through a Rift, and wish to survive by taking over the corpses.

"The Unquiet Dead" is the first episode of the revival to be set in the past, and was intended to show the series' range. The original brief and script included a focus on mediums and was grimmer in tone, but it evolved into a story about zombies and became more of a "romp". Callow, who had researched Dickens as well as portraying him on multiple occasions, accepted the guest starring role in "The Unquiet Dead" because he felt the historical figure was written accurately. The episode also introduced the Cardiff Rift. The episode also features a guest appearance by actress Eve Myles; Myles would go on to play Gwen Cooper in the Doctor Who spin-off series Torchwood from 2006. As contemporary Cardiff, location of the Doctor Who production, did not have enough Victorian architecture, location work for the episode was filmed in Swansea and Monmouth in September 2004 and Penarth in September and October, though one location scene was shot in Cardiff in September. Studio work was recorded at the Unit Q2 warehouse in Newport in September and October.

Computer-generated imagery (CGI) was used as the main visual effect for the Gelth. "The Unquiet Dead" was seen by 8.86 million viewers in the United Kingdom on first broadcast. It attracted generally positive reception, although some reviewers criticised some plot points and lack of moral dilemma.