10 Best 'Star Trek: Original Series' Episodes of All Time, Ranked

Ask 10 Star Trek fans to name the best episodes from The Original Series , and you're likely to get 10 completely different lists. Some will prioritize the writing, others the performances or the science-fiction concepts. And inevitably, somebody will argue that "The City on the Edge of Forever" belongs at No. 1. They might even be right.

When Star Trek premiered in 1966, it offered something different from most science-fiction television of its era. Sure, there were strange alien worlds, futuristic technology and the occasional space battle, but creator Gene Roddenberry also used those adventures to explore morality, prejudice, humanity and what it means to do the right thing.

Nearly 60 years later, the best episodes continue to resonate because they combine those ambitious ideas with unforgettable moments. Not every episode on this list is perfect, but each offers something that helps explain why the original series remains essential science-fiction television.

10 "Court Martial" (Season 1, Episode 21)

Captain James T. Kirk (William Shatner) is accustomed to making life-and-death decisions, but in "Court Martial," it's his own career on the line. Accused of negligence following the apparent death of a crewman, Benjamin Finney (Richard Webb), Kirk faces a military trial in which the Enterprise's computer records contradict his account of what happened.

What makes "Court Martial" memorable is how effectively it turns Star Trek into a courtroom drama. Samuel T. Cogley (Elisha Cook Jr.), Kirk's wonderfully old-fashioned attorney, passionately argues for human rights in an increasingly computerized society. The eventual discovery of Finney, whose heartbeat gives away his hiding place aboard the Enterprise, provides a satisfying conclusion. It's proof that Star Trek doesn't need an alien threat to tell a compelling story.

9 "The Enterprise Incident" (Season 3, Episode 2)

Star Trek rarely ventures into espionage territory as effectively as it does in "The Enterprise Incident." Kirk seemingly loses his judgment and orders the Enterprise into Romulan territory, where Spock (Leonard Nimoy) appears to betray him. Meanwhile, a Romulan commander (Joanne Linville) develops a personal interest in the Vulcan first officer. The elaborate deception eventually reveals itself as a Federation mission to steal a Romulan cloaking device.

The episode works because its characters operate in shades of gray. Kirk resorts to deception, Spock manipulates the commander's trust, and the Romulans emerge as something more than faceless enemies. Linville is especially effective as an intelligent, formidable adversary. There's also the wonderfully ridiculous "Vulcan death grip," a technique Spock admits doesn't actually exist.

8 "The Cage" (Original unaired pilot)

Before Kirk, McCoy or most of the familiar Enterprise crew, there's Captain Christopher Pike (Jeffrey Hunter). In Star Trek's original pilot, Pike is a weary commander questioning his future in Starfleet. When the Enterprise investigates a distress signal from Talos IV, he's imprisoned by aliens capable of creating elaborate illusions that challenge his understanding of reality.

NBC famously rejected "The Cage" as a pilot, but watching it today reveals how much of the franchise's identity was already present. Its somber atmosphere differs from the series that eventually reached television, yet its questions about freedom, perception and human nature are unmistakably Trek. Although footage later appears in "The Menagerie," this fascinating early version of Star Trek deserves recognition on its own merits.

7 "The Empath" (Season 3, Episode 12)

Few Star Trek episodes look or feel quite like "The Empath." Kirk, Spock, and Dr. McCoy (DeForest Kelley) investigate a research station on a doomed planet, only to become prisoners of mysterious aliens called Vians. There they encounter Gem (Kathryn Hays), a mute woman capable of absorbing another person's injuries and suffering.

Much of the episode unfolds against nearly empty backgrounds, giving it the appearance of a stage production. Hays delivers an expressive performance without speaking a word, while McCoy provides the emotional centerpiece when he secretly sacrifices himself to protect his friends. The episode's exploration of compassion and selflessness makes it one of the original series' most unusual and haunting hours.

6 "The Trouble with Tribbles" (Season 2, Episode 15)

Not every great Star Trek episode needs a philosophical dilemma. Sometimes a spaceship full of rapidly reproducing furry creatures is enough. When the Enterprise visits Deep Space Station K-7 to protect a shipment of valuable grain, Uhura (Nichelle Nichols) acquires an adorable creature called a tribble. Unfortunately, tribbles multiply at an astonishing rate, creating chaos aboard the ship and the station.

David Gerrold's script is among the funniest in the original series, balancing the infestation with Klingon troublemaking and Kirk's increasing exasperation. The image of Kirk being buried beneath an avalanche of tribbles remains one of the franchise's most recognizable moments. It's a reminder that Star Trek's characters can be just as entertaining when they're dealing with something ridiculous.

5 "Arena" (Season 1, Episode 19)

"Arena" introduces one of Star Trek's most recognizable alien adversaries, even if the Gorn captain's rubbery appearance has inspired decades of jokes. After an attack on a Federation outpost, Kirk pursues the responsible vessel, only for a powerful alien civilization called the Metrons to intervene. Kirk and the Gorn captain are transported to a barren planet and ordered to fight to the death.

Their confrontation has become legendary, particularly Kirk's improvised cannon and the Gorn's lumbering movements. But the episode's defining moment comes when Kirk gains the advantage and refuses to kill his helpless opponent. His decision transforms a revenge story into something quintessentially Star Trek – the recognition that understanding and mercy can accomplish more than violence.

4 "Space Seed" (Season 1, Episode 23)

Long before Star Trek II: The Wrath of Khan, the Enterprise discovers the SS Botany Bay, an ancient spacecraft carrying genetically engineered humans in suspended animation. Their leader, Khan Noonien Singh (Ricardo Montalbán), is a charismatic tyrant from Earth's past who wastes little time attempting to seize control of the Enterprise.

Montalbán's performance makes "Space Seed" unforgettable. His Khan is intelligent, physically imposing and effortlessly charming, making his battle of wills with Kirk particularly entertaining. The episode also explores the dangers of genetic superiority and the temptation to confuse exceptional ability with moral authority. Kirk's decision to leave Khan and his followers on Ceti Alpha V eventually sets the stage for one of science fiction's greatest films.

3 "The Doomsday Machine" (Season 2, Episode 6)

"The Doomsday Machine" introduces one of Star Trek's most terrifying threats: an enormous automated weapon capable of destroying entire planets. When the Enterprise discovers the damaged USS Constellation, its commander, Commodore Matt Decker (William Windom), is devastated by the loss of his crew. Consumed by grief and revenge, Decker becomes obsessed with destroying the machine, regardless of the danger to everyone around him.

Windom delivers an extraordinary performance, particularly during Decker's confrontation with Spock over command of the Enterprise. His decision to pilot a shuttlecraft directly into the machine is equally unforgettable. With Kirk stranded aboard the Constellation and the Enterprise facing an apparently unstoppable enemy, the episode delivers some of the original series' most intense suspense.

2 "The City on the Edge of Forever" (Season 1, Episode 29)

Widely regarded as one of Star Trek's finest episodes, "The City on the Edge of Forever" sends Kirk and Spock into 1930s New York after a delirious McCoy accidentally alters history. While attempting to restore the timeline, Kirk falls in love with Edith Keeler (Joan Collins), a compassionate social worker whose idealism makes her an especially appealing match for the captain. Unfortunately, Spock discovers that Edith must die for history to unfold correctly.

Shatner delivers one of his strongest performances, particularly during the heartbreaking conclusion when Kirk prevents McCoy from saving Edith. Collins brings warmth and intelligence to a character whose death feels genuinely tragic. It's a devastating exploration of sacrifice, demonstrating that doing the right thing sometimes comes at an unbearable personal cost.

1 "Amok Time" (Season 2, Episode 1)

Spock's Vulcan heritage is central to Star Trek, but "Amok Time" finally takes viewers to his home planet. When Spock begins behaving erratically, McCoy discovers that his condition is life-threatening. Spock reveals that he's experiencing pon farr, a biological cycle requiring him to return to Vulcan. Once there, his intended bride, T'Pring (Arlene Martel), invokes an ancient ritual that forces Spock into combat with Kirk.

There's so much here that has become inseparable from Star Trek's identity, from the introduction of Vulcan traditions to Gerald Fried's unforgettable fight music. But the episode's finest moment comes when Spock, believing he's killed Kirk, discovers his friend is alive and responds with an astonishing burst of happiness. In that brief instant, Nimoy reveals more about Spock's humanity than pages of dialogue ever could. It's a perfect example of why the friendship between Kirk and Spock remains the heart of Star Trek.