First episode to establish the United Federation of Planets as the principal service to which the Enterprise operated under. In previous episodes, vague and often conflicting references were made to this service. Such references included "Space Command", "Space Central", the "Star Service", and "United Earth Space Probe Agency" (the latter even abbreviated as UESPA, pronounced by Captain Kirk as "you spah" in Star Trek: Charlie X (1966)). UESPA would later go on to be the principal service to which the Enterprise NX-01 operated under on Star Trek: Enterprise (2001), which is set in a time when the Federation has not been firmly established.
Scotty's refusal to lower the shields against orders is based on an actual story from James Doohan's military service. As a lieutenant in the Royal Canadian Artillery, he was threatened with court martial for real for saying "No sir, I will not," to a visiting colonel when he realized a training exercise order would entail blowing the heads off some of his own men. Fortunately, his immediate superiors backed him up and, like his fictional character, he was eventually promoted to captain.
In his memoir, "Beam Me Up, Scotty," James Doohan described Gene Lyons (Ambassador Robert Fox), as being "out of his element" and "completely discombobulated" during filming. He added that it took Lyons many takes to get his lines right, and that they finally "went to having him speak off-screen." Doohan speculates that Lyons, who was an experienced actor, may have been thrown off by the science fiction element, as such shows were relatively rare at the time.
Spock refers to himself in this episode as a "Vulcanian" rather than a Vulcan, one of very few times in the series where the longer synonym is spoken. Also, the Enterprise's protection is called screens rather than shields.
Another beautiful matte painting was created for this episode by Albert Whitlock. Unfortunately, it is the last painting in the series into which live actors were inserted. This matte of the Eminiar city was re-used as the backdrop of Scalos in the third season episode Star Trek: Wink of an Eye (1968).
Spock mentions the telepathic capabilities found "among Vulcanians." In Star Trek: Mudd's Women (1966), Harry Mudd referred to Spock as "part Vulcanian." Spock also uses the term "Vulcanian" in Star Trek: Court Martial (1967). Later episodes identified them as Vulcans.
The inner slipcase, along with the fold-out episode guide, from the 2004 DVD release of Star Trek: The Original Series - Complete Season One, featured a large still image on the front cover of Captain Kirk and Mr. Spock which is taken from the ending of this episode.
Bantam Books published a series of novelizations called "foto-novels," which took photographic stills from actual episodes and arranged word balloons and text over them, to create a comic book formatted story. The fourth instalment was an adaptation of this episode.
This episode was assigned to be filmed as Production #23, and "Space Seed" as Production #24. However, as problems arose with the script, needed to be solved by further re-writing by Gene Coon, the staff switched productions with Star Trek: Space Seed (1967), whose script was in a shootable condition. This resulted in "Space Seed" being filmed first, before this one. However, the switch was so quick, they never bothered to change the production numbers, therefore it was believed for decades that this episode was filmed first. Clapperboard images from both episodes also confirm that "Space Seed" was the first to be filmed.
The computer banks on Eminiar VII are also used in Starbase Operations in Star Trek: The Menagerie: Part I (1966) and aboard the shuttlecraft in Star Trek: The Immunity Syndrome (1968). The necked viewscreens used on Eminiar VII are the same ones that appear on the ship in the two pilots and in Mendez's office in The Menagerie.
When Mea 3 escorts the landing party from the beam-down area to the council chamber, the transition of scenes is conveyed not through a cut or a dissolve, but through a wipe - the only time such an effect was used in the original series. Also, this is the only time anyone is able to determine where a person or group of people will materialize.
Anan 7's sash seems to be the same material as the Klingon vest. Similarly, Ambassador Fox's aide appears to be wearing the suit later worn by Arne Darvin in Star Trek: The Trouble with Tribbles (1967).