All the regulars on the show were quitting smoking at the same time, so many chewed gum instead. Director Joseph Pevney was becoming increasingly upset because he had to cut to remind the cast not to chew gum during the shoots. As a prank for a large scene, William Shatner went around handing out bubble gum to the cast, crew, and 60-80 extras, and had everyone blow a bubble right after the director hollered "Action." Sid Haig reported the director "almost passed out." (Source: Sid Haig's phone interview with "The Shlocky Horror Picture Show" for a television airing of Spider Baby or, the Maddest Story Ever Told (1967).)
Contains the first mention of the Prime Directive of noninterference, which the plot brings up only so that Kirk can violate it.
The location scenes for this episode were filmed at the 40 Acres backlot in Culver City, the same place where Miri (1966) and The City on the Edge of Forever (1967) were shot. Best known for their use as Mayberry in The Andy Griffith Show (1960), the sets on this section of the backlot were originally constructed to portray 19th century Atlanta for Gone with the Wind (1939).
In the dungeon when Kirk and Spock subdue Landru's guards, Spock punches the guard in the face with his fist instead of using the Vulcan neck pinch. Kirk even comments: "Isn't that old-fashioned?" This is the first instance of Spock hitting another character in the face with his fist.