* 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 [[http://en.wikipedia.org/wiki/Hudson_v._McMillian this article]] on Wiki/TheOtherWiki.
* CreatorCouple: Gerry and Sylvia Anderson.
** 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 the reason that Barry Morse quit after the first season, and the second became more action-oriented.
** As the leader of a group of aliens heading to Earth in "Earthbound", Creator/ChristopherLee is cast, for once, in a sympathetic role.
** "Death's Other Dominion" has Creator/BrianBlessed playing the straight man to John Shrapnel's hammy ravings. You read that right, Creator/BrianBlessed GIVES THE MORE RESTRAINED PERFORMANCE.
* RealLifeRelative: In addition to being former costars on ''Series/MissionImpossible'', Landau and Bain were husband and wife.
* TechnologyMarchesOn: The Alphans' Commlocks: a combination of portable computer, communicator, TrackingDevice, 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.
* TroubledProduction: 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 ''[[TrashTheSet 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").
* WhatCouldHaveBeen: 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.
* YouLookFamiliar: 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 [[MsFanservice beautiful]] [[RubberForeheadAliens alien]] [[VoluntaryShapeshifting metamorph]] Maya.
** Creator/BrianBlessed 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.