- The series has the unusual distinction of being mentioned in a U.S. Supreme Court decision, in the case of Hudson v. McMillian, 503 U.S. 1 (1992), where Justice Clarence Thomas quoted from an earlier Seventh Circuit decision., Williams v. Boles by Judge Frank Easterbrook (the context was less than complimentary, however, as watching reruns of the show was mentioned as a form of torture). See this article on The Other Wiki.
- The Cameo: A fair number, but one of the more unexpected was Patrick Troughton as the leader of "The Dorcons."
- Creator Couple: Gerry and Sylvia Anderson.
- Executive Meddling:
- Anderson wanted to make a fairly straight space-colony science-fiction show. Then the executives asked if there would ever be stories set on Earth. He said probably. They said they weren't willing to allow that. Hence the much-maligned setup with the moon being blown out of orbit.
- Anderson was originally planning to make a second season of UFO, entitled UFO:1999, set 19 years after the original series. The idea was that the fight against the aliens had intensified and the defensive moonbase had been greatly expanded. Falling ratings for UFO in the States led to ITC cancelling the second season during pre-production, at which point Anderson suggested salvaging something by redeveloping it as an entirely different series. However, it's certainly correct that ITC insisted that some means should be contrived by which no stories could be set on Earth.
- Meddling with the writing was also one of the reasons that Barry Morse quit after the first season, and the second became more action-oriented. Other reasons for him leaving were the extremely long shooting schedule, the quality of the scripts, the lack of time devoted by the producers to developing the characters as opposed to hardware, and finally money. In his autobiography he claims that he wasn't given any information about Bergman's back story, so he had to invent it all himself in order to have something to work with in creating the character.
- Playing Against Type:
- As the leader of a group of aliens heading to Earth in "Earthbound", Christopher Lee is cast, for once, in a sympathetic role.
- "Death's Other Dominion" has BRIAN BLESSED playing the straight man to John Shrapnel's hammy ravings. You read that right, BRIAN BLESSED GIVES THE MORE RESTRAINED PERFORMANCE.
- Real-Life Relative: In addition to being former costars on Mission: Impossible, Landau and Bain were husband and wife.
- Technology Marches On: The Alphans' Commlocks: a combination of portable computer, communicator, Tracking Device, identification item and security key are essentially a somewhat bulkier version of today's smartphones with that consumer item taking on nearly all those functions and more.
- Troubled Production: Suffice to say, it had its moments. As an example, the story goes that the model that portrayed the titular "Infernal Machine" was so literally infernal to manipulate, that the special effects artist tossed it across the room when the final take with it was done.
- Typecasting: The one villain who was undoubtedly played for laughs was cast and voiced by Bernard Cribbins ("Brian the Brain").
- What Could Have Been: Alan Carter was supposed to be the protagonist of the memorable episode Dragon's Domain, achieving personal vindication by killing the monster at the second encounter. Martin Landau had it changed so Carter's role went to a guest actor, and Koenig killed the monster. Adding injury to insult, Carter gets beaten unconscious twice in the episode, which seems rather mean.
- The Wiki Rule: Moonbase Alpha.
- You Look Familiar: Multiple instances; but no guest plays more than two different characters.
- Most notably, Catherine Schell guest-stars in the first-season episode "Guardian of Piri"; then in the second season joins the regular cast as beautiful alien metamorph Maya.
- BRIAN BLESSED plays Dr. Cabot Rowland in an episode of the first season (dying at the end of it), then returns in the second season to play Maya's father (and dies again).
- Isla Blair and Stuart Damon also play two different characters each.
Trivia / Space: 1999