Kirk and Uhura's kiss

In the "Plato's Stepchildren" episode of Star Trek: The Original Series, first broadcast November 22, 1968, Uhura and Captain Kirk kiss. The episode is popularly cited as the first example of a scripted inter-racial kiss on United States television, although other previous instances have since come to light. It post-dates the first interracial kiss on television by nearly a decade, as an interracial kiss was broadcast on February 1, 1959, in the UK on the ITV Armchair Theatre adaptation of Ted Willis's play Hot Summer Night.
Originally, the scene was meant to be filmed with and without the kiss, so that the network could later decide whether to air the kiss. However, Shatner and Nichols deliberately flubbed every take of the shot without the kiss so that the shot could not be used.
The episode features a kiss between James T. Kirk (William Shatner) and Lt. Uhura (Nichelle Nichols) which is often—and incorrectly—described as the first scripted interracial kiss on American television. The first interracial kiss on television seems to have occurred years earlier on British television in the play Hot Summer Night, broadcast in early 1959. A later broadcast,You in Your Small Corner, featured a kiss between black actor Lloyd Reckord and white actress Elizabeth MacLennan, and was broadcast live on the UK's ITV channel in June 1962. Another such kiss occurred in 1966, when The Wild Wild West, James T. West (Robert Conrad) and Princess Ching Ling (Pilar Seurat), shared a white and Asian interracial kiss ("The Night the Dragon Screamed", aired 1966 Jan 14). In the same year on I Spy, Kelly Robinson (Robert Culp) and Sam (France Nuyen) also had a white and Asian interracial kiss ("The Tiger", aired 1966 Jan 5). There had also been a kiss between Sammy Davis, Jr. and Nancy Sinatra on Movin' with Nancy in 1967, a year before "Plato's Stepchildren" aired.
The episode portrays the kiss as involuntary, being forced by telekinesis, perhaps to avoid any hint of romance that would risk outrage among some viewers. Also, William Shatner recalls in Star Trek Memories that NBC insisted their lips never touch (the technique of turning their heads away from the camera was used to conceal this). However, Nichelle Nichols insists in her autobiography Beyond Uhura (written in 1994 after Shatner's book) that the kiss was real, even in takes where her head obscures their lips.
When NBC executives learned of the kiss they became concerned it would anger TV stations in the Deep South. Earlier in 1968, NBC had expressed similar concern over a musical sequence in a Petula Clark special in which she touched Harry Belafonte's arm, a moment cited as the first occasion of direct physical contact on American television between a man and woman of different races. At one point during negotiations, the idea was brought up of having Spock kiss Uhura instead (as Spock was half Vulcan), but William Shatner insisted that they stick with the original script. NBC finally ordered that two versions of the scene be shot—one where Kirk and Uhura kissed and one where they did not. Having successfully recorded the former version of the scene, Shatner and Nichelle Nichols deliberately flubbed every take of the latter version, thus forcing the episode to go out with the kiss intact.
As Nichelle Nichols writes:

Knowing that Gene was determined to air the real kiss, Bill shook me and hissed menacingly in his best ham-fisted Kirkian staccato delivery, "I! WON'T! KISS! YOU! I! WON'T! KISS! YOU!"
It was absolutely awful, and we were hysterical and ecstatic. The director was beside himself, and still determined to get the kissless shot. So we did it again, and it seemed to be fine. "Cut! Print! That's a wrap!"
The next day they screened the dailies, and although I rarely attended them, I couldn't miss this one. Everyone watched as Kirk and Uhura kissed and kissed and kissed. And I'd like to set the record straight: Although Kirk and Uhura fought it, they did kiss in every single scene. When the non-kissing scene came on, everyone in the room cracked up. The last shot, which looked okay on the set, actually had Bill wildly crossing his eyes. It was so corny and just plain bad it was unusable. The only alternative was to cut out the scene altogether, but that was impossible to do without ruining the entire episode. Finally, the guys in charge relented: "To hell with it. Let's go with the kiss." I guess they figured we were going to be cancelled in a few months anyway. And so the kiss stayed.
There were, however, few contemporary records of any complaints commenting on the scene. Nichelle Nichols observes that "Plato's Stepchildren" which first aired on November 22, 1968 "received a huge response. We received one of the largest batches of fan mail ever, all of it very positive, with many addressed to me from girls wondering how it felt to kiss Captain Kirk, and many to him from guys wondering the same thing about me. However, almost no one found the kiss offensive" except from a single mildly negative letter from one white Southerner who wrote: "I am totally opposed to the mixing of the races. However, any time a red-blooded American boy like Captain Kirk gets a beautiful dame in his arms that looks like Uhura, he ain't gonna fight it." Nichols notes that "for me, the most memorable episode of our last season was 'Plato's Stepchildren.'"