A crossover is a story in which elements from two fictional universes, originally created to be distinct, are brought together for the span of a specific narrative.
There have been many crossovers between stories officially set in the Doctor Who universe and other works of fiction, some licensed on the part of the property being crossed over with, some not. Some use devices such as the Land of Fiction to allow characters from the DWU to "meet" individuals who are, otherwise, as fictional to them as to the reader.
However, many crossovers imply that the property being crossed over with is actually a part of the DWU, even if that was not that property's creators' original intent. Others make use of the idea of the Multiverse to establish the Doctor's home dimension as distinct from, but coexisting with, other dimensions inabited by various unrelated fictional characters.
By definition, only stories licensed to use the DWU concepts they contain are covered on this Wiki. The following crossovers are, however, notable for also having been licensed appearances of the "foreign" concepts with which the DWU characters interact. They were usually advertised as crossovers.
- The earliest planned televised crossover was in the 1965 episode "The Feast of Steven", in which the Doctor Who production team hoped to use the main cast and setting of Z-Cars for some scenes set in a police station. However, Z-Cars producer David Rose rejected the idea. The plan was referenced in the novelisation, which named the policemen after the Z-Cars cast.
- The earliest, albeit minor, released crossover between the DWU and another fictional property occurred in 1966 in Thunderbirds, on ITV rather than the BBC, as a tie-in with the magazine TV Century 21, which published the Daleks comic serials under the guise of being in-universe reports produced in the 2060s within the shared universe of Gerry Anderson's science fiction TV series. One of these reports was clearly seen, although briefly, on-screen in a close-up in the Thundebirds episode The Man from MI.5, with the word "DALEK", the image of a War Machine Dalek and that of the Golden Emperor all visible.
- The final episode of Season 3 of Out of the Unknown, entitled Get Off My Cloud, was an official crossover with Doctor Who through a metafictional device: the main character became trapped in a dream world where he was menaced by Daleks drawn from his nightmares, nightmares developed from watching Doctor Who itself. He eventually summoned the Doctor's TARDIS ("played" by the actual TV prop used at the time in Patrick Troughton's TV stories) inside the dream realm as part of his efforts to defend himself.
- In both TV: The Pirate Planet and Destiny of the Daleks, both written by Douglas Adams, the Fourth Doctor mentions several elements from Adams' The Hitchhiker's Guide to the Galaxy.
- TV: The Visitation featured the character Richard Mace, who had previously appeared in three BBC Radio Drama plays by Eric Saward from 1974 to 1976.
- In a 1986 Roland Rat television story, the Sixth Doctor appeared and expressed his distaste for the series.
- In the 1993 Children in Need special Dimensions in Time, the Doctor and some of his companions met the cast of EastEnders as part of the show's 30th anniversary celebrations. (Notably, this special is not considered a valid source on this Wiki.)
- Sandra Mitchell from Russell T Davies' show Children's Ward briefly appeared in The Long Game.
- Although not a crossover with another fictional property, Bad Wolf functioned as a legal crossover between Doctor Who and the reality TV shows and game shows Big Brother and The Weakest Link, with the music, logos and (in some cases) performers of these shows being lawfully hired to portray the futuristic versions of themselves produced on the Game Station.
- One Born Every Minute, broadcast as part of the the 2013 Comic Relief telethon, saw the Eleventh Doctor transporting the cast of the BBC Drama Call the Midwife through time.
- Dermot and the Doctor, broadcast as part of the National Television Awards, featured not only another crossover with EastEnders (with another appearance of Dot Cotton) but also a crossover with Coronation Street in the character of Becky McDonald.
- BBC Christmas indents featuring the Doctor have sometimes featured joking crossovers with other BBC shows on several occasions: the 2010 BBC Christmas ident was a crossover with Come Fly with Me; and the 2012 BBC Christmas ident It's Showtime featured another crossover with Call the Midwife and Agnes Brown from the BBC sitcom Mrs Brown's Boys.
- Sprout Boy meets a Galaxy of Stars crossed over with many BBC characters such as John Luther from Luther, Sherlock Holmes with John Watson from BBC's Sherlock, and Dot Cotton from EastEnders for the third time.
- Mind My Minions was also a crossover, this time with Despicable Me spin off Minions and for the second time Coronation Street.
- Looking for Pudsey crossed-over many reality shows, including Strictly Come Dancing and The Great British Bake Off, and one scripted show: Call the Midwife, with Jenny Agutter reprising her character.
- The Family Guy season 15 episode Inside Family Guy contained a licensed crossover appearance by the Tenth Doctor, with David Tennant reprising his role, in a cutaway scene in which the Griffin family watch a TV story titled Doctor Who Farted. The episode aired on Fox (a brief return to the network for the franchise since the TV movie twenty years prior) in the US, and on ITV2 in the UK.
- In the earliest-known crossover between Doctor Who and another fiction franchise to have been fully licensed on both sides, a 1965 issue of Radio Times published a comic strip in which the cast of Captain Pugwash crossed paths with the First Doctor.
- In the context of the TV Century 21 magazine, characters and concepts from The Daleks frequently crossed over with series like Thunderbirds, Stingray, Fireball XL5, and 21 (and vice versa).
- When Marvel UK owned Doctor Who Monthly (later Doctor Who Magazine), characters like Death's Head, Keepsake, and the Special Executive sometimes crossed over into the wider Marvel Multiverse.
- In 2012, IDW published Star Trek: The Next Generation/Doctor Who: Assimilation², a crossover between Doctor Who and Star Trek: The Next Generation.
- In a a short comic story released in 1991 as promotion for the Comic Relief charity event, Dan Dare encountered the first seven incarnations of the Doctor and several companions.
- In an interesting case, Big Finish's Vienna Salvatori made her debut in the Doctor Who story The Shadow Heart before her own series was launched, making The Shadow Heart a retroactive crossover. Vienna reappeared in a mainline DWU work in Master!, where she acted as the antagonist to the Master' villain-protagonist.
- Likewise, Dorian Gray debuted in the Bernice Summerfield audio Shades of Gray.
- Both Vienna and Dorian Gray, as well as Big Finish's Sherlock Holmes, crossed over with elements of the Doctor Who universe in The Worlds of Big Finish.
- Big Finish's Cicero, played by Samuel Barnett, crossed over with the Fifth Doctor's world in Tartarus.
- Return of the Queen was a crossover between Iain McLaughlin and Claire Bartlett's Erimem and Kerides the Thinker series.
- The Old Ones originated in the Cthulhu Mythos, which pre-dated Doctor Who.
- Iris Wildthyme originated in the independent works of Doctor Who novel writer Paul Magrs.
- Sherlock Holmes and Doctor John Watson appeared as themselves in All-Consuming Fire where they are established as real. (In the Doctor Who universe, they do not actually use the names Sherlock Holmes and Watson, but use these as aliases.) Lord John Roxton from Sir Arthur Conan Doyle's The Lost World also cameos in the same novel.
- In Damaged Goods, the character Marcie Hatter from writer Russell T Davies' television series Dark Season briefly appears as a member of UNIT in 2017.
- Carnell, the psychostrategist featured in Chris Boucher's Corpse Marker, first appeared in the Blake's 7 episode Weapon (where he was portrayed by Scott Fredericks). Fredericks played Carnell once again in the Kaldor City audio series.
- Thomas Carnacki appeared in the Doctor Who novella Foreign Devils and the Iris Wildthyme audio Iris Rides Out.
- Bernice Summerfield character Jason Kane was mentioned in creator Dave Stone's 2006 Judge Dredd novel Psykogeddon.
- In The Coming of the Terraphiles, mention is made of the Conjunction of the Million Spheres, and one of the characters is named Cornelius. Both are connections to author Michael Moorcock's Multiverse stories.
- The prose series 10,000 Dawns had three licensed crossovers (Rachel Survived, White Canvas, and The Gendar Conspiracy) wherein characters from the fictional 10,000 Dawns literally travel between universes to interact with elements of the Doctor Who universe.
- The anthology Cwej: Down the Middle includes multiple stories where Chris Cwej crosses over with elements of other stories, including Jeffrey Koval's Deptford County (PROSE: Fountain of Youth) and the works of Clark Ashton Smith. (PROSE: When I Remember __________) Additionally, Iris Wildthyme made a guest appearance in Flickering Flame. The Surgeon mentions these future encounters while bonding Cwej to the conceptual weapon V-Time, explaining, "And which letter represents the meeting of points better than V? V-Time is thus the conscious weaponization of the crossover."
- Doctor Who was one of 30 different franchises to be represented in the mass-crossover video game LEGO Dimensions.
The following crossovers are usually brief cameos by, or allusions to, elements of non-DWU works of fiction in DWU stories. The non-DWU elements are unlicensed and sometimes not explicitly named.
The following lists are such crossovers as they occurred within stories licensed from the DWU's point of view; however, the symmetrical situation often occurs, with elements of the DWU being acknowledged in other works of fiction. Such unlicensed crossovers are listed as "in-universe references" at Cultural references to the Doctor Who universe.
- In Mindwarp, a Xenomorph chestburster specimen was present in Crozier's laboratory, implying a shared universe with the Alien franchise.
- In Remembrance of the Daleks, Allison Williams wished that Bernard was with them, with Rachel Jensen replying that the British Rocket Group had its own problems. This is a reference to the Quatermass television serials. It was elaborated upon in the short story prelude to Remembrance of the Daleks, Background, where the events of the first two Quatermass serials are explicitly related as real events in the Doctor Who universe, although Quatermass was not named, being referred to as simply "the Director of the British Rocket Group". It was not until the televised Planet of the Dead that the name "Bernard Quatermass" was used in the DWU.
- In the 2003 release of Shada, Arthur Dent, Zaphod Beeblebrox, and a Nutri-Matic Drink Synthesizer are briefly seen.
- In Dalek, a Xenomorph ovomorph (egg) is on display, continuing what was started with Mindwarp.
- In The Christmas Invasion, the Tenth Doctor mentions Arthur Dent in such a fashion as to suggest that they've met. (Arthur Dent was one of the main protagonists of The Hitchhiker's Guide to the Galaxy.) Daniel Llewellyn, a member of the group sent out to meet with the Sycorax Leader, is representing the British Rocket Group from Quatermass.
- In the 2017 release of The Power of the Daleks, the Weyland-Yutani Corporation logo is seen.
- In the 2017 release of Shada, several books that allude to The Hitchhiker's Guide to the Galaxy are seen.
- In Minuet in Hell, the Brigadier mentions the Doomwatch organisation, which first appeared in the 1970s TV series of the same name.
- In the Kaldor City series, already a licensed Blake's 7 crossover through the character of Carnell, references are made to Roj Blake and Travis, the Butcher of Zircaster. Additionally, the main character, Kaston Iago, is hinted to be Kerr Avon.
- Iris Wildthyme and the Land of Wonder featured Iris Wildthyme travelling to Wonderland, as seen in Lewis Carroll's Alice in Wonderland.
- In A Sting in the Tale, the Fourth Doctor mentions Vogons, the Eighth Doctor owned an Altairian dollar in Storm Warning, and in Max Warp, one of the spaceships is described as a "Lazlar Lyricon custom job". All of the these elements are references to The Hitchhiker's Guide to the Galaxy.
- In The Eternal Present, Theophilus Tolliver, a 19th century inventor, time traveller and friend of H.G. Wells is implied to be the protagonist of Wells' The Time Machine, who was known only as the Time Traveller (both characters have the same initials).
- In the Comic Relief Comic — already a licensed crossover between Dan Dare and Doctor Who — a rocket with a white-and-red checkered paintjob is in the background of one panel. This is the iconic Moon rocket from the Franco-Belgian Tintin comics.
- In Party Animals, several characters from other fictional universes are seen in the background: Bart Simpson from The Simpsons; Worf and a Ferengi from Star Trek; Darth Vader from Star Wars; Emma Peel and John Steed from The Avengers; and Sapphire and Steel from the TV series of the same name.
- In Operation Proteus, a newspaper headline reads "Apemen At Knightsbridge". This is a reference to the TV serial Quatermass and the Pit.
- In Endgame, the TARDIS library has books by Christian Storm and Edmund Bancroft, characters from the films Horror Hospital and Horrors of the Black Museum, both of whom were played by Michael Gough. The Celestial Toymaker claims to have beaten Le Chiffre (from the James Bond novel Casino Royale) at baccarat.
- In Fire and Brimstone, Izzy Sinclair describes the book she's reading as featuring a city called Ankh-Morpork, an old hag called Granny Weatherwax, and a whole world the shape of a disc. She asks the Doctor why they can't go somewhere like that and he replies "Izzy, I've been. It was flat." These are all references to the Discworld book series.
- In Spam Filtered, the Doctor says he once knew a hard-light hologram who was a "bit of a jobsworth". This may be a reference to Arnold Rimmer of Red Dwarf.
- In Bazaar Adventures, there was a shop, Babel Fish Aquarium. Babel Fish originate in The Hitchhiker's Guide to the Galaxy.
- The 1995 short story Background built on the reference to the British Rocket Group in Remembrance of the Daleks, explicitly establishing the events of the first two Quatermass serials as having occurred in 1953 and 1955 in the DWU. It is noted that the televised broadcast of the 1953 events was claimed to be a fictional sci-fi TV programme as part of the government cover-up, alluding to Quatermass's real-world status as televised fiction.
- In The Pit, mention is made of the Hob's Lane disaster. This is a reference to the events of the TV serial Quatermass and the Pit.
- In White Darkness, mention is made of the Rihanssu language. In the Star Trek novels, Rihannsu is the name that Romulans use for themselves.
- In No Future, mention is made of a Soviet military group called the Vodyanoi. This is a reference to the David Wiltshire novel Child of Vodyanoi, which was adapted into the TV series The Nightmare Man.
- In The Crystal Bucephalus, Turlough remembers reading about the effects of plasma damage on the biosphere of Qo'noS, the Klingon homeworld in Star Trek.
- In Invasion of the Cat-People, the Doctor mentions the Lion-Men of Mongo (Flash Gordon), Caitians (Star Trek), Kzinti (Larry Niven's Known Space series) and agents of the Aegis (Star Trek).
- In Millennial Rites, there are brief appearances of a man in a blue cloak levitating in an old brownstone in New York, and a blond-haired man in a dirty beige trenchcoat having a Guinness in a Dublin bar. These are meant to be the comic book magicians Doctor Strange and John Constantine.
- In Happy Endings, Bernice meets a teenage girl dressed in black with dark hair who seems familiar to her. The girl says that her job is to turn off the lights once everybody's gone. The girl is intended to be the version of Death from Neil Gaiman's The Sandman.
- In The Death of Art, Anton Jarre recalls meeting a Belgian police sergeant who is clearly intended to be a young Hercule Poirot.
- In The Dying Days, Lady Creighton-Ward (Thunderbirds), Geoffrey Hoyt (Medics) and Emma Knight (The Avengers) appear at a party. Mention is made of a planned nuclear-waste storage facility on the Moon in two years (Space: 1999), the first manned flight to Jupiter two years after that (2001: A Space Odyssey), MI6's double-O agents (James Bond), the IMF (Mission: Impossible), and Omega Sector (True Lies).
- In The Face of the Enemy, mention is made of an English village named Little Storping. A village with the same name appears in "Murdersville", an episode of The Avengers.
- In The Fall of Yquatine, Fitz Kreiner is said to have worked at the Mother Black Cap in Camden Town in the 1960s. This is a reference to the film Withnail and I, which is set in the same time period and features a pub of the same name in the same location.
- In Verdigris, Jo Grant reminisces about her friend Tara, with whom she'd gone to spy school and who was also assistant to an eccentric freelance gentleman adventurer in secret service to the government. This is clearly meant to be Tara King of The Avengers.
- In The Quantum Archangel, mention is made of Oa (from Green Lantern comics), the Shi'ar Empire (from X-Men comics) and Pym particles (from Avengers comics).
- In Eater of Wasps, when the Doctor is asked if he had ever read Tarzan, the Doctor replies that he had met him, too.
- Professor Challenger from The Lost World and Van Helsing from Dracula cameo in Mad Dogs and Englishmen.
- In The Book of the War, the Eremites and their labyrinth are references to the Cenobites from Clive Barker's Hellraiser franchise.
- It was heavily implied in Bide-a-Wee that Susan Foreman had just experienced the events of Five on a Treasure Island, the first book in the The Famous Five series of children's books.
- Warlords of Utopia references various other words of fiction which depict alternate Earths, such as Philip K. Dick's The Man in the High Castle and Robert Harris's Fatherland. It also suggests that in Roma I, I, Claudius was written
- The Indestructible Man includes a large number of thinly-veiled characters, locations, and concepts from the television shows of Gerry Anderson, particularly PRISM (Spectrum), the Indestructible Man (Captain Scarlet), and Global Response (International Rescue).
- In Fear Itself, a character is said to possess a Stradivarius cello called the Lady Rose. A cello of this name and make appeared in the James Bond film The Living Daylights.
- In The Gallifrey Chronicles, a copy of the first Harry Potter novel in the Doctor's TARDIS has the first page crossed out and the words "No, no, no, no, it didn't happen like this at all" written on it in red ink, implying that the Doctor knows how it did happen.
- In Omegamorphosis, mention is made of Gregor Samsa, who turned into an insect, and whose story was written by his friend. This is a reference to The Metamorphosis.
- In Forever Autumn the Doctor claims to have met Jar Jar Binks' clan, and that George Lucas mistook a telepathic message for his own ideas, implying that the Star Wars stories were based on real events.
- In Magic of the Angels, the Doctor has a large carpet bag which is bigger on the inside than the outside, and says that he is glad he got it back from Mary Poppins.
- In The Pneuman League, Strax encounters a young Albert Steptoe from the sitcom Steptoe and Son.
- In Greyhound, Alistair Gordon Lethbridge-Stewart's memoir mentions that David Attenborough visited Darkest Peru for his documentary series Attenborough in the Amazon. Darkest Peru was a fictional area of Peru which was home to Paddington Bear in A Bear Called Paddington.