The first thing you need to know about Star Trek: The Original Series is that it only lasted for three seasons. The second thing you need to know is that there’s a pretty good reason for that. Its catalog of episodes is wildly uneven, with stories that range from the cringeworthy to the simply dull, but the good ones are oh, so very good.
In fact, the impact of the best Star Trek: The Original Series episodes is still being felt by the franchise to this very day. Some introduced characters that would later become legendary, others set a standard for storytelling that any show would be proud to match. Others laid a foundation for concepts, plotlines, or themes that would become part of the immutable essence of what “Star Trek” is.
It’s also worth mentioning that even when Star Trek whiffed, it was because the writers were swinging for the fences. Airing during an unprecedented era of U.S. social history, Star Trek genuinely wanted to give audiences a new way of looking at issues like racism, politics, war, and violence. Sometimes it succeeded, sometimes it didn’t, but there was true nobility in the attempt. And hey, it also made things like “phaser” and “transporter” everyday language, which is also pretty cool.
Even hardcore fans typically agree that revisiting the entire run of Star Trek: TOS isn’t the best use of your time, so here are the ten best Star Trek episodes to watch in order to fully soak up the vibe.
If you're on the other side of the of the Kirk vs Picard debate, then you should check out our guide to the best Star Trek: The Next Generation episodes too.
10. The Tholian Web
- Season 3, Episode 9
- Original airdate: November 15, 1968
The heart of TOS was always the unlikely trio of Kirk, Spock, and McCoy, whose relationship is a tumultuous mix of camaraderie, respect, affection, and frustration. Kirk disappears while the Enterprise is investigating the cause behind the loss of all hands aboard The Defiant, leaving Spock and McCoy to argue about what to do next.
The ship is in jeopardy, but Kirk might still be alive — Spock’s cool logic is naturally at odds with McCoy’s passionate response. Kirk was always the buffer between those two strong personalities, and watching them interact without his calming presence is, as Spock would say, fascinating.
9. The Doomsday Machine
- Season 2, Episode 6
- Original airdate: October 20, 1967
Beneath its sheen of bravado and machismo, Star Trek was ultimately about self-sacrifice for the greater good. Kirk was never hesitant to put himself at risk to protect his crew, a character trait he inherited from his father if the 2009 Kelvin timeline movie is to be believed. The Enterprise discovers The Constellation after its disastrous run-in with a planet killer: a miles-long machine that destroys planets and devours the rubble as fuel. Phasers have no effect on the behemoth, so Kirk devises a plan to fly the Constellation straight down its maw and explode it from within.
Fortunately, Spock and Scotty manage a small alteration to the plan and beam Kirk back to the Enterprise before he meets his maker. The Enterprise has a habit of going toe-to-toe with enormous threats, and the Doomsday Machine is one of the biggest.
8. The Squire of Gothos
- Season 1, Episode 17
- Original airdate: January 12, 1967
The Squire of Gothos walked so that Q could run. A being calling himself General Trelane (retired) starts messing with Kirk and crew for his own amusement. He snatches them from their ship, changes their clothes, even forces them to stand trial — sound familiar?
It’s impossible to watch The Squire of Gothos and not see a direct throughline to John DeLancie’s portrayal of the all-powerful imp who delights in Picard’s frustration. Interestingly, the end of the episode appears to reveal Trelane to be a child (or at least childlike), despite his appearance.
7. Space Seed
- Season 1, Episode 22
- Original airdate: February 16, 1967
If you read our list of Star Trek movies ranked worst to best, you already know why this episode makes the list. Space Seed introduces the one and only Khan Noonien Singh and sets up the action that will later take place in the film The Wrath of Khan.
The Enterprise comes across Khan and his followers in stasis. Upon their revival, they attempt to take over the Enterprise. Their plan is foiled and Kirk exiles them to Ceti Alpha V…and we all know what happens next. Even if it didn’t precede such a phenomenal film, Space Seed would make this list as an example of how fast and loose Kirk often plays with others’ lives.
6. Amok Time
- Season 2, Episode 1
- Original airdate: September 15, 1967
First appearance of Pavel Chekov and the very first glimpse of Vulcan? Even if neither of those happened, Amok Time would still make this list for being one of many examples of Kirk being willing to to defy Starfleet in order to save his crew, and Spock in particular.
Kirk requests permission to take the Enterprise to Vulcan because Spock is in the grips of pon farr, the “mate or die” condition unique to Vulcans. On Vulcan, Spock’s intended demands that he fight a champion of her choosing in order to prove he deserves her — and then she selects Kirk. Ever seen Cable Guy? Yep, this is what that’s parodying.
5. The Menagerie Pts 1 & 2
- Season 1, Episodes 11 & 12
- Original airdate: November 17 & 24, 1966
Star Trek’s beginning was a little messy. Its first pilot (yes, there was more than one) featured Captain Pike, not Kirk, in an episode called The Cage. The Menagerie cleverly repackages that episode as Spock recalling events that took place when he served under Captain Pike — a relationship recreated first in Star Trek Discovery and more recently in Strange New Worlds.
Majel Barrett, who would go on to not just be the voice of the Enterprise computer but also Counselor Troi’s mum, stars as Pike’s first officer, Number One. Few episodes of TOS passed on as many different kinds of legacy as The Menagerie.
4. Arena
- Season 1, Episode 18
- Original airdate: January 19, 1967
Arena features one of Star Trek’s most frequently visited recurring themes: humanity’s propensity for violence. An unknown vessel fires upon the Enterprise, which gives chase. Both ships venture into the territory of the Metrons, which decide to settle the matter by pitting Kirk and the other vessel’s captain against each other in one-on-one combat. The winner’s ship gets to go free, the loser, not so much.
The other captain is the reptilian Gorn who Kirk fells after cobbling together a bazooka out of bamboo and rocks; if you were ever wondering where the “rudimentary lathe” joke from Galaxy Quest came from, now you know. When Kirk spares the Gorn’s life, the Metrons decide maybe there’s hope for humanity after all (another constant Star Trek refrain) and allow both ships to go free.
3. The Trouble With Tribbles
- Season 2, Episode 15
- Original airdate: Dec 29, 1967
Star Trek: TOS tackled plenty of serious social issues across its three seasons, but it wasn’t afraid to be funny, too. The Trouble With Tribbles is pure sitcom as the crew of the Enterprise discovers, adores, and then is slowly overtaken by the furry, purring creatures of the title.
Kirk alternately sits on one that’s found its way to the Captain’s chair, then finds himself buried in them after opening an overhead compartment. It’s a low-stakes, iconic romp that would later be revisited in the Deep Space Nine episode Trials and Tribble-ations.
2. Mirror, Mirror
- Season 2, Episode 4
- Original airdate: October 6, 1967
A transporter malfunction swaps Kirk, McCoy, Scotty, and Uhura with their “evil” selves from the mirror universe, a totalitarian hellscape that would be revisited thematically, if not actually, in virtually every iteration of Trek to follow.
The crew of the ISS Enterprise and that of the USS Enterprise both work to discover why their crewmates aren’t quite themselves and then, upon sussing the answer, send them home. It’s a fun episode in and of itself, but a must-have on the list given the impact it would end up having.
1. The City on the Edge of Forever
- Season 1, Episode 28
- Original airdate: April 6, 1967
This may be the best-known episode of TOS. Harlan Ellison pitched the idea and wrote the first version of the story, but the rewrites from Gene Roddenberry (among others) made him hate the eventual script so much he asked to have his name struck from it. Ellison would continue to loudly complain about on City of the Edge of Forever for the rest of his career, but the episode is still an all-time great.
McCoy, drugged out of his mind, stumbles through a time portal and winds up changing the timeline. The Guardian of Forever allows Kirk and Spock to go through the portal after him in an attempt to clean things up. While visiting Earth’s past, Kirk falls in love with Edith Keeler, unforgettably played by Joan Collins. Too late, he discovers the event that changes the future: McCoy saving Edith’s life.
Kirk being forced to let her die in order to preserve the future is a personal tragedy that underscores that beneath the phasers, transporters, subspace anomalies, and cranial ridges, Star Trek is about exploring what it means to be human.
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