Over its five decades, no science-fiction property has had more of an effect on the genre than Star Trek. Five television series, an animated cartoon, and a dozen movies have captivated Trekkies for generations. While the show has occasionally produced some kitschy dialogue and plot lines that are cringe-worthy, there are many episodes that withstand the test of time as some of the greatest sci-fi adventures ever put on a screen.
In preparation for the forthcoming new series from CBS, Star Trek: Discovery, we glossed hundreds of episodes from each live-action series and picked some of our favorites for you to enjoy, whether you’re new to the franchise or a life-long fan. We’re sure this will cause a lot of discussion, but if you really want to go where no sci-fi adventure has gone before, here are the 20 episodes you’ll want on your watch list.
Star Trek: The Original Series
Set in the 23rd century, Star Trek: TOS follows the five-year mission of the USS Enterprise, with Captain James T. Kirk (William Shatner), first officer and half-Vulcan Spock, the ever cantankerous ship’s Doctor Leonard McCoy (DeForest Kelly), Uhuru (Nichelle Nichols), Sulu (George Takei), and the rest of the gang, alongside a host of alien species.
Season 1, episode 28: The City on the Edge of Forever
The final episode of the original series’ first season gets our nod for its solid storyline. Some of the episodes of TOS seemed to suffer from gimmicky — if not corny — plots, but Roddenberry and his team thread the needle well in this one. In fact, it was good enough to receive the 1968 Hugo (the Emmys of sci-fi) for Best Dramatic Presentation.
In this episode, Kirk and Spock must travel back in time to go after McCoy, who, in a fit of delusion following an accidental overdose of Cordrazine, transports down to the nearest planet. This planet is home to a time portal, and McCoy enters the portal. The incident alters the time line, causing the Enterprise and the entire Federation to disappear. Kirk and Spock bargain with the “Guardian of Forever” to enter the portal, which takes them back to 1930s New York City. What unfolds is a story about timelines that might have been, a device later used by J.J. Abrams in the series’ cinematic reboot.
Season 2, episode 4: Mirror, Mirror
Another alternate timeline story, this one again traps our heroes in an alternate reality. An ion storm sends Kirk, chief engineer Montgomery “Scotty” Scott, McCoy and communications officer Uhura to a parallel universe where the Terran Empire replaces the Federation. The alternate reality replaces the Enterprise’s mission of peace and exploration to one of conquest, and ascending in rank means killing your commanding officer.
Season 1, episode 22: Space Seed
No list of the best TOS episodes would be complete without the greatest Trek villain of them all, Khan Noonien Singh. The Enterprise stumbles upon Khan’s ship, the SS Botany Bay, and renders assistance. Little do they know, however, that Khan is the leader of a group of superhumans left over from the Eugenics Wars — a fight over genetic engineering. Before long, Kirk is fighting for his ship and possibly the future of the Federation against a man who is much stronger, smarter, and cunning than he. Khaaaaaaan!
Season 2, episode 15: The Trouble With Tribbles
This episode does have the kind of gimmicky and corny plot we bemoaned earlier. However, The Trouble with Tribbles is one of those episodes that just makes you smile, if only for the reactions of the crew to the seemingly unlimited reproductive capabilities of these furry (and cute) little creatures.
Star Trek: The Next Generation
Set approximately 80 years after the original Trek, The Next Generation takes viewers aboard an all new Enterprise in a completely different (and generally more peaceful) Federation. The Enterprise “D” is captained by Jean Luc Picard (Patrick Stewart) with his trusty “Number One” Commander William T. Riker (Jonathan Frakes) by his side. All new challenges and powerful new alien species await the new crew.
Season 3, episode 26/Season 4, episode 1: The Best of Both Worlds
For many Star Trek fans, this two-part episode ranks as one of the best of any of the series, if only for its full introduction to the Borg — a ‘race’ that is really a singular consciousness host organism controlling multiple beings (although they appear briefly in the second season episode “Q Who”). Some may also argue this is where TNG itself turned around – its first two seasons had many forgettable storylines and often weak character development. But as the third season progressed, the stories got better and the characters did too, with the season ending in grand fashion thanks to this cliffhanger.
The Borg attack the Enterprise after responding to a distress call, and in the process kidnap Picard. There’s a reason for this: the Borg want to assimilate the Human race, and Picard has all the Starfleet knowledge they need to do it. Sensing defeat, the Enterprise crew attempts a last ditch effort to capture Picard, eventually succeeding. While Picard comes through physically unscathed, the traumatic experience haunts our captain for the rest of his life. It’s a storyline that is often returned to throughout the rest of the show’s run.
Season 3, episode 23: Sarek
Occasionally Star Trek takes a break from the space drama storylines in an attempt at a more heady plot. This often fails, but Sarek nails it. Sarek is Spock’s father, who is well into the throws of Bendi Syndrome when the crew meets him, a disease that causes otherwise nearly emotionless Vulcans to broadcast emotions onto others (Vulcan’s thousands of years before Trek learned how to suppress and control their emotions). Sarek needs to achieve emotional peace to negotiate a peace treaty with the Legarians, so a mind meld is needed with an emotionally stable person to make this possible. Picard agrees, but he also ends up having to deal with all of Sarek’s extreme emotional instability – and Vulcans hide deep intense emotions even in good health. Perhaps it’s Patrick Stewart’s Shakespearian actor background, but he really sells it.
Season 3, episode 15: Yesterday’s Enterprise
Star Trek loves time travel, and that’s what Yesterday’s Enterprise is all about. In this instance, though, how the episode accomplishes the trick is pretty slick. The real timeline Enterprise encounters a rift in the space-time continuum, but when the ship passes through, the timeline shifts in a dramatic way. The Enterprise is now a warship, and the Federation is near defeat in a bloody war with the Klingons. In this new timeline, Klingon Security office Worf isn’t there – instead replaced by Tasha Yar, the ship’s security officer killed in the first season (In the movies and after TOS, the Klingons struck a peace deal with the Federation). Only Guinan — the ship’s ‘bartender’ in the Ten Forward lounge and part of a race with psychic like powers –know something’s wrong here, and knows that the ship must go back to make everything right.
Season 2, episode 9: The Measure of a Man
For Data fans, this episode is a sure-fire favorite. Data, the seminal example of a near human android and the ship’s science officer — is involved in a dispute between scientist Commander Bruce Maddox, who wants Data to allow him to download his contents to learn how he works. Data refuses, but Maddox doesn’t give up – instead he goes to a Starfleet judge and asks for Data to be ordered to comply on the grounds he isn’t human. Picard asks for a trial, which is granted, but Riker must act as the prosecutor in the case. In the end, we find ourselves questioning consciousness and asking what it really means to be “human.”
Star Trek: Deep Space Nine
Deep Space Nine takes place around the same time as TNG, although later episodes take place after TNG‘s run. DS9 is the only Trek so far to take place somewhere other than a starship, set instead on a starbase commanded by Commander Benjamin Sisko (Avery Brooks) and Bajorian liason Major Kira Nerys (Nana Vistor). Specifically, Deep Space Nine takes place on a Cardassian starbase orbiting Bajor, a new Federation ally. The Cardassians enslaved the Bajorans for decades, and their quick withdraw left Bajor in shambles. However, the only stable known wormhole is located close by Bajor presenting a problem not only for the Federation and Bajor, but also for the rest of the galaxy.
Season 6, episode 19: In The Pale Moonlight
Much of the latter part of DS9 revolves around the Federation conflict with the ultra-powerful Dominion, who live on the other side of the wormhole across the galaxy. The storyline is also a departure from the previous two series in which most of the episodes stood alone (although there certainly were carried themes). What we like most about this particular episode is the fact that it deals with some very relatable issues: morality and the true costs of war.
With the Dominion War putting a huge stress on Federation resources, Commander Sisko looks to Garak — a former Cardassian spy that now lives aboard DS9 — to convince the Romulans that they’re next. There’s only one problem: there’s no real evidence of this. Garak and Sisko attempt to forge evidence, but that fails as well. In the process to ensure his plan works, Garak installs a bomb on the Romulan ship that visits the station, which departs quickly once the crew realizes the evidence is fake. As the ship leaves, it explodes – which Sisko obviously takes issue with. Sisko confronts Garak, but Garak tells Sisko that when the wreckage is scanned it will still implicate the Dominion, and the fact that the Dominion will protest vigorously only further convinces the Romulans of their guilt. It works, and the Romulans join the Federation in the fight, a turning point in the long and bloody war.
Season 1, episode 19: Duet
This episode arguably set the tone for the rest of DS9’s seven-year run, and highlighted the scars of occupation between Bajor and Cardassia. The 19th episode of the first season, the primary subjects here are Kira Nerys and a Cardassian Aamin Marritza, who has contracted Kalla-Nohra, a deadly disease that’s a result of the Bajoran-Cardassian occupation and its mining efforts. While Deep Space Nine’s Chief Medical Officer Dr. Bashir doesn’t recognize it, Major Kira knows the disease can only be from a brutal labor camp called Gallitep that she liberated, where those involved in a mining accident contracted Kalla-Nohra. Marritza must have been part of the Cardassian security force that kept the Bajorans enslaved. Can Kira look past this?
Season 4, episode 3: The Visitor
Time travel appears again and again in Star Trek, but The Visitor is a bit different. An accident while observing a rare inversion of the Bajoran wormhole from aboard the Defiant — the DS9’s own warship that was a staple of later seasons — leaves Captain Sisko frozen in time. While the crew believes him to be dead, he later starts appearing for brief moments, and at the next occurrence of the inversion, son Jake Sisko attempts to save his father.
Season 7, episodes 25 and 26: What You Leave Behind
The series’ two-part finale had a tough job to do. With a story arc that focuses a lot more on existential topics that any of its peers, giving Deep Space Nine a proper ending wasn’t exactly the easiest thing to do. But the Dominion War needed an end, and its characters a just conclusion. That includes Sisko’s storyline as the “emissary” — Bajor’s religious community thinks Sisko is the prophecy of a Bajoran renaissance incarnated. Despite these challenges, the episode wraps things up quite beautifully, making for a fitting end to Star Trek’s most unconventional series.
Star Trek: Voyager
Like DS9, Voyager is also set around the same time period as Star Trek: The Next Generation. Things start out normal for the crew of the starship Voyager, but a chance (or perhaps not so chance) encounter with super-advanced technology from the other side of the galaxy flings the ship 70 light years away from home. How does Captain Kathryn Janeway (Kate Mulgrew) and the crew find their way home? The answer is the underlying storyline of the entire series.
Season 4, episodes 8 and 9: Year of Hell
Kathryn Janeway and crew are often overlooked over when it comes to Trek, but the vessel’s location so far from the Federation gave writers wide latitude in trying out new storylines and new villains. Perhaps the best of those villains is Annorax, a genocidal Krenim who has the power to change the timeline.
Annorax’s starship creates temporal incursions which allow him to erase entire civilizations with a powerful weapon. His goal is to strengthen his race, but each time he does so, it causes even more problems. One incursion causes a plague that kills millions of Krenim including his wife, but it also affects the Voyager, too.
In two parts that span the course of a year in this alternate timeline, Voyager and crew battle the Krenim, leaving the ship all but useless. Out of options, Janeway decides to order the crew to abandon ship, and theorizes the only way the Krenim can be stopped and the timeline restored is if the Krenim timeship itself is destroyed while creating another incursion. It’s an intriguing plot that keeps viewers in suspense.
Season 5, episode 26/Season 6, episode 1: Equinox
Another two-part episode, this one deals with how things could have turned out for Voyager if circumstances were different. We find out here that Voyager wasn’t the only Federation ship to be swept away to the Delta Quadrant by the Caretaker, the name of the advanced technology we touched on in the synopsis. But the crew of the other ship isn’t the same as that of the Voyager, and they harbor a dark secret that includes the torture of an alien race to power a quicker way home.
Season 4, episode 23: Living Witness
This episode stands on its own as one of Voyager’s best because it shows how history can be revised to serve a political purpose (sound familiar?). The episode revolves around The Doctor, a holographic being designed as an emergency pair of hands that ends up being the ships full time doctor. The character is reactivated after 700 years, only to find out he’s no longer on the ship. Instead, he’s on a planet that knows about Voyager, but has painted them in an unflattering light. Can the Doctor fix history, while also helping to save this civilization?
Season 3, episode 26/Season 4, episode 1: Scorpion
Even though it was so far away from home, Voyager still seemed to lean back on older storylines and even villains (such as Voyager being flung towards the Borg’s neck of the galactic woods). This two-part series introduces the super powerful and hardly humanoid Species 8472, along with new crew member Seven of Nine. The two additions change the path of the series for its final three seasons, bringing on a darker, grittier Voyager.
Star Trek: Enterprise
Enterprise is set in a time period much closer to ours, the 22nd Century. It follows the original Enterprise vessel, Earth’s first starship designed for exploration, which is captained by Jonathan Archer (Scott Bakula). Much of the series revolves around explaining how future Trek storylines came to be, including meeting some of the property’s most memorable races and villains. While not widely acclaimed, those who want to know the whole storyline will want to give Enterprise a chance.
Season 3, episodes 23 and 24: Countdown and Zero Hour
Picking a best episode for Enterprise is difficult. Like TOS, it ran for a much shorter time than other series in the canon, and the show just never seemed to find its place in the Trek universe. Many of the storylines involve episodes melding into one another, so many of our picks here are two parters. These two episodes are a great example of what the series could have been, creating a dramatic end to the Xindi — a conglomerate of alien races that believe Earth is a direct threat to them. The Xindi are assisted by aliens from the future, and the storyline is visited throughout much of the series.
Here, Archer and crew finally figure out where the Xindi are storing their super weapon, which is found to be destined for Earth. While the crew is successful in destroying the weapon, they find themselves returning to a very different Earth. You’ll need to watch season 4’s StormFront episodes to understand the entire story, and the story does seem to break down unfortunately in its second half. Still, these two chapters are very intriguing.
Season 4, episode 18: In a Mirror, Darkly parts 1 and 2
One set of episodes that doesn’t follow the continuing storyline convention to create a “standalone” storyline is In a Mirror, Darkly (it’s actually a two-parter). If you’re a fan of The Next Generation’s alternate reality episode Yesterdays Enterprise, and especially our TOS pick Mirror, Mirror, you’re going to want to put this double shot of episodes on your watch list.
Season 1, episode 7: The Andorian Incident
The inclusion of this episode is sure to rile the feathers of some Trek purists. Enterprise is oft criticized for its less-than-flattering presentation of the Vulcans — who have always been presented as the do-gooders of the Trek Universe — and many point to this episode as one of the biggest offenders. Here we find out the Vulcans are spying on the Andorians, and are using a sacred sanctuary as cover for their shady work. Bad, bad Vulcans.
Season 1, episodes 1 and 2: Broken Bow
The two hour premiere of the show is definitely one of the better ones. It’s a neat look into the early days of the Federation, and arguably lays out a lot more character development for the cast than other Trek series did early on.
That’s our list! We’re sure this will spark plenty of debate about which episodes and even which series are the best of the franchise, but that’s part of the fun! No matter which episodes you love best, all of them relish in humankind’s enduring desire to boldly go … well, you know the rest.
- The 79 best shows on Hulu right now
- The best TV shows on Amazon Prime Video right now
- Stuck in a time loop: The best TV episodes and movies that keep repeating the same day
- How to watch the Star Trek movies and TV shows in order
- Star Trek Day ’21 celebrates 55 years of Kirk and beyond with livestreamed event