Five particular episodes of Star Trek: The Original Series are masterpieces that not only defined the first Star Trek show but also laid the foundation that has allowed Gene Roddenberry’s franchise to soar for the next sixty years.
Star Trek only aired for three seasons on NBC from 1966 to 1969. Never a ratings hit in its day, Star Trek was on the brink of cancellation and was saved by passionate fans writing letters to the network. After Star Trek left network TV, however, it became a phenomenon in syndication.
As of 2025, there are now 12 Star Trek TV series as well as 14 Star Trek movies. The multitudes of characters, starships, and voyages throughout the final frontier are all based upon the original five-year mission of Captain James T. Kirk’s (William Shatner) Starship Enterprise.
In truth, not every hour of Star Trek’s original 78-episode run is a winner. There are many bad episodes, or mediocre outings, in Star Trek: The Original Series’ three seasons, and a number of very good episodes, as well.
Yet when the original Star Trek was great, it was truly great, and those episodes remain iconic decades later. The following Star Trek: The Original Series episodes are true masterpieces that still color modern Star Trek, as well as being all-time classic hours of TV.
“The Trouble With Tribbles”
Star Trek: The Original Series Season 2, Episode 15
“The Trouble With Tribbles” was a risk when it aired in 1967, but it successfully proved that Star Trek could be a comedy where audiences laughed along with the crew of the USS Enterprise, not at them.
Captain Kirk was never more hilariously irritated than when the Starship Enterprise is diverted to space station K-7 to protect a shipment of valuable grain from the Klingons. Meanwhile, the real threat was the seemingly innocuous, furry Tribbles.
A comedic romp that allowed the innate humor in Star Trek to take center stage, “The Trouble With Tribbles” introduced the iconic fuzzballs that dangerously multiply when fed, and featured William Campbell as the effete Klingon, Captain Koloth.
Star Trek: Deep Space Nine season 5 did a sequel called “Trials and Tribble-ations” that seamlessly placed Captain Benjamin Sisko (Avery Brooks) and his crew into “The Trouble With Tribbles,” cementing how iconic the original is.
“The Devil in the Dark”
Star Trek: The Original Series Season 1, Episode 25
Cited by both William Shatner and Leonard Nimoy as their favorite Star Trek episode, “The Devil in the Dark” is a hallmark of Star Trek’s core values of making contact and understanding those you would perceive to be your enemies.
When the USS Enterprise is diverted to the mining colony of Janus VI, Captain Kirk and Mr. Spock (Leonard Nimoy) learn that a creature called a Horta is responsible for the deaths of several miners.
Instead of killing the Horta, Spock mind-melds with the silicone-based alien, discovering it is a female and a mother who was protecting its eggs, which the miners were destroying.
“The Devil in the Dark” depicts one of the most powerful instances of Spock using his Vulcan mind-meld, and this Star Trek masterpiece is a riveting morality play with a thought-provoking lesson about understanding and coexistence.
“Amok Time”
Star Trek: The Original Series Season 2, Episode 1
Star Trek: The Original Series season 2 kicked off with the series’ most thorough exploration of Mr. Spock’s life and Vulcan culture to date, as the Science Officer diverts the Starship Enterprise back to his homeworld.
“Amok Time” introduced T’Pau (Celia Lovsky), one of the elder leaders of Vulcan. A younger version of T’Pau (Kara Zediker) appeared in Star Trek: Enterprise season 4.
“Amok Time” is a landmark episode that introduced the Vulcans’ seven-year mating cycle, pon farr, the Vulcan ritual combat kal-if-fee, and revealed that Spock was engaged since childhood to T’Pring (Arlene Martel), who wanted to break their betrothal to marry another Vulcan.
T’Pring chooses Captain Kirk to be her champion and battle Spock to the death, with the Science Officer believing he killed his best friend. Spock’s genuine shock and relief to find Kirk alive is one of his most heartwarming moments.
Star Trek: Strange New Worlds reintoduced T’Pring (Gia Sandhu) and explored her relationship with Lt. Spock (Ethan Peck) in better days for the couple, as well as homaged Spock’s battle with Kirk in a dream sequence where Vulcan Spock fought his human half.
“Balance of Terror”
Star Trek: The Original Series Season 1, Episode 14
“Balance of Terror” is one of the most pulse-pounding and riveting episodes of Star Trek: The Original Series, or any Star Trek for that matter.
Introducing the Romulans, who would go on to become one of Star Trek’s most enduring and iconic alien villains, “Balance of Terror” is a Star Trek version of a classic cat-and-mouse submarine movie like Run Silent, Run Deep.
The revelation that the Romulans are genetic offshoots of the Vulcans injected a powerful debate about prejudice and racism, as one Starship Enterprise crewman casts suspicion on Mr. Spock as “one of them.”
Mark Lenard, who would go on to portray Spock’s father, Ambassador Sarek, debuts as the Romulan Commander, who tests all of his skills against Captain James T. Kirk, and ends up defeated by but respecting his Starfleet counterpart.
Star Trek: Strange New Worlds’ season 1 finale remade “Balance of Terror,” placing Captain Christopher Pike (Anson Mount) in Kirk’s shoes with vastly different results, reinforcing how pivotal Kirk is to the fate of the galaxy.
“The City on the Edge of Forever”
Star Trek: The Original Series Season 1, Episode 28
For nearly 60 years, “The City on the Edge of Forever” has held the status of ‘greatest Star Trek episode ever,’ and the star-crossed love story between Captain Kirk and Sister Edith Keeler (Joan Collins) proves why it deserves that praise with each viewing.
Captain Kirk and Mr. Spock time travel to 1930s New York to find Dr. Leonard McCoy (DeForest Kelley) turned mad, and they learn Edith Keeler’s death is the focal point that decides Star Trek’s future. Edith Keeler must die, but Kirk has fallen in love with her.
Written by Harlan Ellison, the version of “The City on the Edge of Forever” that aired after several revisions is markedly different from the combative author’s original intent, yet the episode retains its power to tug at the heartstrings as Kirk gives up the love of his life to preserve the fate of the universe.