With the iconic science-fiction franchise Star Trek coming to Paramount+ in its entirety, now is the perfect time for old fans to revisit and new viewers to introduce themselves to the series that started the global phenomenon as it celebrates its 55th anniversary this year. With three seasons totaling nearly eighty episodes in all, diving into the series can be a little intimidating for new audiences can be a bit intimidating but, fortunately, we have got you covered.

Listed below are the ten best, viewer-friendly episodes from the classic original series. The episodes are listed in the order of the dates in which they first aired rather than based on the quality of the entries themselves.

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Balance of Terror

While Starfleet and the United Federation of Planets were established early on as a largely peaceful, utopian society, the organization found itself in a heated conflict with several rival civilizations, the first being the Romulan Star Empire. Introduced in the Season 1 episode "Balance of Terror," the Enterprise investigated outposts attacked by a mysterious force along the border between the Federation and the Romulans.

"Balance of Terror" not only introduces audiences to the Romulans but also their similarities to the Vulcans, causing one xenophobic crewman to express suspicions regarding Spock. And even apart from what the episode introduces to the franchise, it also serves as an early example of starship combat in deep space as the crew faces an invisible enemy.

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Arena

The Federation has explored and colonized worlds out in the far reaches of the unknown and this comes back to explosively haunt them in the Season 1 episode "Arena." As the Enterprise visits a border colony, they are shocked to discover it destroyed by an attacking force known as the Gorn. Pursuing the attackers deep into uncharted space, Kirk and the Gorn captain are transported to a remote planet by an omnipotent being to duel to the death.

"Arena" is an episode that not only packs plenty of action but also beautifully showcases the Federation's mission statement of bringing peace to strange, new worlds, even when under direct attack. It also demonstrates just how resourceful Kirk is, forced to think quickly and draw in real-world science when faced against a far physically superior opponent.

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Space Seed

If there's one individual antagonist that is most closely linked to the entire Star Trek franchise, it's Khan Noonien Singh. Memorably portrayed by Ricardo Montalban in the Season 1 episode "Space Seed" and the acclaimed 1982 film Star Trek II: The Wrath of Khan, the Kelvin timeline would attempt to introduce their own spin on the classic rivalry between Khan and the Enterprise in 2013's Star Trek Into Darkness, portrayed by Benedict Cumberbatch.

For Montalban's fantastic first performance as the instantly classic villain not only provides Captain Kirk and the crew with a worthy adversary but also perfectly sets up a rewatch of Wrath of Khan, exploring a plot thread that had gone on unresolved for fifteen years.

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Errand of Mercy

Kor (left) faces off with Kirk in "Errand of Mercy."

Just as the first season introduced the Romulans, it also introduced the more prominent antagonists for the Federation, the Klingon Empire. As a fresh round of negotiations for peace between the Federation and Klingons collapse and war is declared, the Enterprise finds itself on the frontlines as it moves to defend the peaceful world of Organia on the Klingon border from a sweeping invasion.

In addition to introducing one of the most iconic alien species in all of Star Trek with the Klingons, "Errand of Mercy" is perhaps the strongest episode in the original series to focus on the antagonism between Starfleet and the Klingon Empire. And while a tentative ceasefire is reached, the real-world Cold War parallels between the two civilizations would be further explored throughout the remainder of the series.

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The City on the Edge of Forever

One of the most widely praised episodes of any Star Trek series is Season 1's penultimate episode "The City on the Edge of Forever." A temporarily crazed Doctor McCoy travels back to 1930s America where he inadvertently changes history, forcing Kirk and Spock to retrieve him and restore the timeline.

"The City on the Edge of Forever" really shows how emotional and tragic Star Trek can truly be at times, with some of the best acting and writing the series has ever delivered. Immediately accessible for new audiences, there's a reason why this specific episode has continued to resonate across the franchise for over fifty years.

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Amok Time

Star Trek's Kirk and Spock battle in a scene from Amok Time

The emotional core of the original Star Trek series and run of feature films really is the friendship between Kirk and Spock as they explore the wonders of the cosmos while defending the Federation. This friendship would lethally be put to the test in the Season 2 premiere episode "Amok Time" as Spock's Vulcan biology made him grow erratically violent as part of the Vulcan mating cycle.

"Amok Time" is the first serious, deep-dive into Spock's Vulcan heritage, culminating in the two friends pitted in a fight to the death as part of the ancient ceremony. And through it all, the episode contains some of Leonard Nimoy's finest work in the series and showcases just how important Spock and Vulcans are to the overall Star Trek mythos.

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Mirror, Mirror

MIRROR MIRROR STAR TREK

One of the most recurring tropes across Star Trek is the existence of a morally inverted Mirror Universe, where the peaceful Federation and Starfleet were reimagined as the militaristic Terran Empire. After a transporter accident sends Kirk and the rest of his landing party to the Mirror Universe, they must elude familiar faces looking to kill them while searching for a way back to their dimension.

The Season 2 episode "Mirror, Mirror" not only introduces the Mirror Universe to the franchise but also is one of the best episodes in the series. Following the original series, the Mirror Universe would play a prominent part in Star Trek: Deep Space Nine, Enterprise and Star Trek: Discovery as a testament to the episode's impact on the mythos.

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The Doomsday Machine

As a product of the Cold War, one of Star Trek's most impressive episodes that drew inspiration straight from contemporary headlines was the Season 2 episode "The Doomsday Machine." As the Enterprise investigates the wreckage of a fellow Starfleet vessel, they stumble across a planet-killing device developed by warring civilizations before their arms race literally consumed them.

While the production design of the eponymous doomsday machine may be a bit dated, even with the remastered edition of the original series, the episode delivers Cold War parallels without being overly preachy and remembers to bring in the epic starship-based action as the Enterprise makes its last stand.

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Journey to Babel

While Spock's parents and their respective occupations had been mentioned in passing in the original series' first season, both characters would make a memorable appearance in the Season 2 episode "Journey to Babel." When the Enterprise hosts a contingent of ambassadors, including Spock's father Sarek and his mother Amanda, a lot of tension is brought aboard the ship.

Detailing Spock's complicated dynamic with his father while giving Kirk and McCoy plenty to do to keep the diplomatic mission from going off-the-rails, "Journey to Babel" brings the action, drama and fun in an excellent showcase of what the series is capable of.

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The Trouble with Tribbles

Star Trek: Trouble With Tribbles

For all the hard sci-fi and philosophical musings Star Trek is capable of, it's also a show that's well-aware how far out there it can be and occasionally leans into the more comedic possibilities of its premise to great effect. The most memorable instance of the more humorous explorations of the original series is in the Season 2 episode "The Trouble with Tribbles."

While visiting a Federation space station, the Enterprise discovers the station is overrun with a small, rapidly reproducing lifeform known as a Tribble, which quickly spreads to the ship. And as Kirk and the crew search for a way to deal with the growing Tribble population, they have to contend with the arrival of the Klingons at the station. In terms of balancing stakes and laughs, no episode in the original series does it better than "The Trouble with Tribbles."

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