Each issue of TV21 was formatted so as to pass itself off as a news magazine printed exactly one hundred years in the future. Although some stories taking place in the 20th century were presented in the magazine, they were printed in black and white, and presented as "archival documents" or footage from a time machine.
In accordance with its format, TV21 was written with the intent that all the stories and articles printed within describe a single fictional future history of the solar system. Although it mainly featured comic strip stories based on the puppet television creations of Gerry Anderson, the first 104 TV21 issues also subsumed several elements of the Doctor Who universe into this "merged canon", licensed not from the BBC but from individual rightsholders Terry Nation and David Whitaker.
The most famous consequence of this was The Daleks (later reprinted as The Dalek Chronicles), a comic serial written by David Whitaker. It constituted one of the earliest licensed Doctor Who spin-offs, as the Doctor did not appear in these stories; concurrent with the publishing of The Daleks, the rights to the character were with Polystyle Publications, Ltd., the publishers of TV Comic. Polystyle created new recurring antagonists, the Trods, to replace the Daleks, who would ultimately be shown being exterminated by the actual Daleks in The Trodos Ambush when TV21's license expired and the Daleks were once again allowed to face Dr. Who in comics as they did on television. In the meantime, The Daleks instead revealed the early history of the Dalek Empire, starting with an origin story for the species and continuing through the Golden Emperor's first wars of conquest on the universe until the start of Daleks' Invasion Earth 2150 A.D.
In addition to Terry Nation's Daleks and Mechanoids, another licensed DWU concept was introduced to TV21 fiction: the planet Astra, which had been created by David Whitaker in TV: The Rescue as part of the background of new companion Vicki Pallister. Astra was referenced in The Daleks and became central to further crossovers with other Anderson-based TV21 strips.
Two further unique interactions occurred between TV21 and the Doctor Who universe. The first came when Issue 28 of the magazine tied in with the release of Dr. Who and the Daleks, the first Peter Cushing feature film, by presenting a cover story and a special Lady Penelope short story which both referenced the film as existing in-universe; The Story of the Film, a short prose adaptation of the movie itself; and a parody, Film Star Wins Oscar—Misses Premier!, featuring "Doctor Da and the Humanies".
After the end of The Daleks in January 1967, TV21 underwent several mergers with other comic publications. It subsumed TV Tornado in 1968 and became known as TV21 and Tornado; it also absorbed Joe 90 magazine in 1969, following which it was known as TV21 and Joe 90 for 37 issues. The end of the TV21 and Joe 90 run coincided with the end of Gerry Anderson-based content in the magazine. Finally, in 1971, after 347 total issues, TV21 was itself merged into Valiant magazine, which was temporarily known as TV21 and Valiant as a result. Valiant joined Battle Picture Weekly in 1976, which in 1988 was merged into Eagle. Eagle ultimately ended in 1994.
Due to its "newspaper from the future" framing device, instead of a conventional magazine cover, the cover of the publication contained prose fiction in the shape of a newspaper front-page article. These prose stories usually tied into the narratives of the ongoing comic serials; as such, many of them featured the Daleks alongside content from the Stingray and Fireball XL5 strips, essentially serving as early crossovers between the DWU and the Gerry Anderson universe.
- "Daleks in the 21st Century - An introduction to The Dalek Chronicles", DW50Y 1
- The Knowledge Emporium: The Rise and Fall of TV 21