Over the course of its five-decade-plus history on television, the enduring Star Trek franchise has told hundreds of important stories wrapped in sci-fi trappings across an ever-expanding slate of series. The sheer volume of tales can be daunting for newcomers, often lured by a taste of one of the latest streaming series or falling for one of the films, looking to plunge deeper into the mythology. 

Since the earliest days of the original 1960s series, Star Trek has long been hailed for its ability to deliver pointed social commentary under the guise of its futuristic setting and otherworldly characters. But it's also successfully incorporated other genres and styles ranging from high comedy to whodunnits, traditional courtroom dramas, and the season-long story arcs currently favored. Additionally, built-in conceits including time travel and the Holodeck open all every imaginable corner of history. 

Zeroing in on standout installments is a challenge, with each series delivering its share of excellent entries over time. But with an eye toward those stories that, along with being wildly entertaining yarns, have proven to provide definitive examples of various enduring aspects of what Gene Roddenberry's storied sci-fi franchise is all about — and occasionally episodes that somehow successfully break all the established rules — here, Metacritic presents a dozen of Star Trek's most memorable episodes (just in time for a new series to begin!), in chronological order of release.

Arena

Star Trek: The Original Series (Season 1, Episode 18)
Best for: Fans of action, creatures, and old-school special effects 
Where to watch:

There's a reason why the iconography of this episode — in which godlike beings force Kirk (William Shatner) and his opposing captain from the reptilian Gorn to engage in mano-a-lizard combat on a desolate planet to prove which race is more worthy — still looms so vividly: it's packed with visceral fighting action by the very game Shatner, brains prove more valuable than brawn, and there's the baked-in message about mercy still resonates. Come for all that, but stay for creature designer Wah Chang's still-creepy Gorn creation. 

The Devil In the Dark

Star Trek: The Original Series (Season 1, Episode 25)
Best for: Fans of sci-fi parables, mysteries, and creatures
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The parable potential of the Star Trek franchise is on full display — along with its beating, humanist, inclusive heart — in this engrossing story by Trek's second key "father," Gene L. Coon. As the Enterprise crew tracks the Horta, a craggy, rock-like creature that's been wreaking havoc on a space mining colony, Spock (Leonard Nimoy) resorts to a Vulcan mind-meld to unravel the mystery behind its aggression. The results are both a great plot twist and a key component of Star Trek: only by better understanding those we fear can we make peace with them. 

The City On the Edge of Forever

Star Trek: The Original Series (Season 1, Episode 28)
Best for: Fans of time travel, love stories, and Shatner
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Sci-fi legend Harlan Ellison's imaginative time-travel plot (finessed by franchise creator Roddenberry) is the unchallenged ne plus ultra of episodic Star Trek. In it, Kirk and Spock, searching for a time-lost McCoy in the Depression era 1930s, encounter benevolent, selfless Edith Keeler (Joan Collins), and Kirk falls hard for her. Collins and Shatner — disarmingly underplaying Kirk as besotted romantic — have charming chemistry, while Spock's struggles to stay incognito and frustration with cruse technology provide amusement, and that heartbreaking final act twist — in which Kirk's selfless actions define putting the needs of the many over the needs of the one long before it became a much-quoted Spock mantra — is as genuinely startling as it is affectively poignant. It's not just classic Star Trek; it's classic television, full stop. 

Amok Time

Star Trek: The Original Series (Season 2, Episode 1)
Best for: Fans of Kirk and Spock, action, and Vulcans
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Star Trek's first major glimpse into the genuine alienness of the logic-driven Vulcan culture and its surprisingly savage customs comes when an overriding biological urge sends Spock back to his home planet to marry his long-betrothed, only to be manipulated into a duel to the death with his captain. A highlight of the franchise's inventive, thought-out depictions of otherworldly races and featuring one of the franchise's all-time great fight sequences, this entry is seminal to depicting the deepening bonds between Kirk, Spock, and McCoy (DeForest Kelley).  

Mirror, Mirror

Star Trek: The Original Series (Season 2, Episode 4)
Best for: Fans of alternate universes 
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Five decades before it became the trope du jour in pop culture, the sci-fi notion of alternate, wildly diverging realities went mainstream with this clever episode that uses a transporter malfunction to thrust Kirk and an away team into a malignant dimension where Starfleet is an evil, conquering empire populated by twisted, scheming versions of their crewmen, like the bearded Spock and scarred Sulu (George Takei). Such good, nasty fun that it made the concept of the Mirror Universe a staple across several Star Trek series. 

The Measure of a Man

Star Trek: The Next Generation (Season 2, Episode 9)
Best for: Fans of artificial intelligence, courtroom dramas, and Data (Brent Spiner)
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After a bumpy first season, Star Trek: The Next Generation (TNG) began finding its footing, and then some, with this excellent exploration of Data. He's an artificial being, but should that mean he is the property of Starfleet, or deserving of self-determination? Adapting TV's tried-and-true courtroom format to hash out the arguments, the episode employs allegories of slavery, existential questions of existence, and legal oratory well-delivered by a fiery Picard (Patrick Stewart), while Spiner's performance as Data locks his status as this series' unique mirror on humanity and its foibles. 

Yesterday's Enterprise

Star Trek: The Next Generation (Season 3, Episode 15) 
Best for: Fans of time travel, love stories, and space battles
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This cleverly crafted alternate timeline tale makes great use of the much-loved sci-fi conceit when the Enterprise-D's long-lost predecessor Enterprise-C emerges from a chronal rift and, by surviving a past battle with the Klingons, alters history, for better (Tasha Yar, played by Denise Crosby, is alive and well on the Bridge again) and worse (the Federation is badly losing its war with the Klingons). From that dystopian twist comes a rousing and even romantic rush to the end, where characters must make hard decisions about what they'll do to make things right again.  

The Best of Both Worlds (Part I and Part II)

Star Trek: The Next Generation (Season 3, Episode 26 and Season 4, Episode 1) 
Best for: Fans of space battles, action, The Borg, and Picard 
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TNG brings the cinematic scope and scale of the Star Trek films to the small screen with this tense nail-biter that defines just how dangerous and terrifying the relentless Borg collective could be. The two-part episode also provides quite the cliffhanger, leaving off at the end of the third season when viewers had to wait months to see the start of the new season. (But now you can just start the next episode up in binge fashion and admittedly some of the tension fades quickly.) Still, the image of the seeming unbeatable Picard as the assimilated Locutus provokes terror in viewers' hearts. Not only is it a rip-roaring episode, Picard's ego-leveling trauma will haunt him for decades to come in other key storylines, such as Star Trek: First Contact and the follow-up series Star Trek: Picard. 

The Inner Light

Star Trek: The Next Generation (Season 5, Episode 25)
Best for: Fans of thoughtful sci-fi, character drama, and Stewart as an actor
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The Hugo Award-winning episode is contemplative and emotional, spinning out of a novel sci-fi conceit: After an encounter with an ancient alien device, Picard experiences a near-lifetime of memories unfolding as a simple farmer on a planet that's dying a slow but certain death, while the Enterprise crew scrambles to free their captain from the probe's influence in real time. Stewart delivers a subtle tour de force performance as Picard lives out the other man's memories and makes deep emotional connections to the doomed world, artfully expressed in a coda that's one of the franchise's most moving moments. 

Far Beyond the Stars

Star Trek: Deep Space Nine (DS9) (Season 6, Episode 13)
Best for: Fans of time travel, social commentary, and Sisko (Avery Brooks)
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The achingly poignant story not only sets aside space and special effects for the most part, it shows that Star Trek doesn't always need to cloak its social commentary in allegorical clothing: it confronts the torment of racism head on when Sisko's (Brooks) hallucinates a second life as Benny Russell, an aspiring 1950s sci-fi writer determined to get his story with a Black protagonist in print, only to be thwarted by institutionalized discrimination at every turn, with an anguished conclusion in which Brooks, who also directs, is at his most riveting. 

In the Pale Moonlight

Star Trek: Deep Space Nine (Season 6, Episode 19)
Best for: Fans of political intrigue, moral dilemmas, Brooks as an actor
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Brooks is at his very best in this mesmerizing potboiler the finds Sisko traveling down an increasingly slippery slope of challenged ethics and moral compromises in his attempts to turn the neutral Romulans into allies in the ongoing war with the Dominion. (Don't believe us? Sample his monologue about war.) Supporting player Andrew Robinson as the amoral Garak is an ideal foil in Sisko's desperate scheme, and the knockout ending demonstrates just how DS9 successfully takes the franchise into some of its darkest territory, particularly when meditating on the high cost of warfare. 

Scorpion (Part 1 and Part 2) 

Star Trek: Voyager (Season 3, Episode 26 and Season 4, Episode 1)
Best for: Fans of Seven of Nine (Jeri Ryan) and the Borg 
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Just as Voyager finds its storytelling groove, this episode brings Janeway's (Kate Mulgrew) crew into a new conflict with the popular collective baddies The Borg, while simultaneously introducing Species 8472, a new alien race so fearsome and formidable they routinely kick The Borg's behinds. But the main attraction here is the introduction of Ryan's Seven of Nine, the once-human assimilated drone who must work with the crew to fend off the new threat, ultimately becoming a reluctant member of the crew — and a fascinating new character that the show uses to explore new issues of humanity. 

Year of Hell (Part 1 and Part 2)

Star Trek: Voyager (Season 4, Episodes 8 and 9)
Best for: Fans of time travel, epic action, and Janeway 
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OK so maybe there are more than a dozen episodes on this list, technically, because of the two-parters. But this is a rare mid-season two-parter that ups the ante on the action in the series. An encounter with the Zahl, an alien race that uses temporal technology to retroactively change history and build its might, proves catastrophic for Voyager, forcing Janeway and her crew to fight a yearlong battle against an increasingly powerful foe with just a skeleton crew of her top officers. Guest star Kurtwood Smith shines as the Zahl commander, who's revealed to have deeply personal motives for his temporal tampering as the Voyager crew battles to reset the timeline. 

Such Sweet Sorrow (Part 1 and Part 2)

Star Trek: Discovery (Season 2, Episodes 13 and 14)
Best for: fans of Space battles, Star Trek lore 
Where to watch: iTunes,

A newer entry among established classics, this two-parter comes with caveats: Because of Discovery's tightly serialized nature, it works best viewed as part of the larger season — indeed, it's really the culmination of many arcs across the series' first two seasons — including the Klingon War and Michael Burnham's (Sonequa Martin-Green) relationship with her adoptive Vulcan brother Spock (Ethan Peck). Familiarity with The Original Series two-parter/repurposed pilot "The Menagerie" provides additional resonance with the future vision that haunts Pike (Anson Mount, taking full ownership of the role). There's also genuinely epic-scale space battles and a shocking twist ending — the latter a massive gamechanger for the entire series.