(written from a Production point of view)
With Star Trek having narrowly avoided cancellation, the basic format remained the same as Season 2. The season opened with "Spock's Brain", a story in which Kara, the priestess-leader of the underground Eymorg city, steals Spock's brain and transfers it to a receptacle so that he can rule their society.
Other episodes continued to serve as political parables. "Day of the Dove" carried a strong anti-war message, while "Let That Be Your Last Battlefield" dealt with racial hatred, ending with the Enterprise unable to prevent the destruction of a civilization or even dissuade the two survivors from continuing their feud. "The Empath" told a tightly constructed morality play with Kirk, Spock, and McCoy teach an alien woman the value of self-sacrifice. "Plato's Stepchildren" may not have featured television's first interracial kiss as is often claimed, but was still groundbreaking enough to be banned in some states.
Kirk had one of his most significant romances in "The Paradise Syndrome", as he spent three months stranded on a planet, fell in love, and married, only for his pregnant wife to be killed in a tragic misunderstanding. He also fell in love with an android in "Requiem for Methuselah", inadvertently bringing about her death. Spock attracted female attention in episodes like "The Enterprise Incident", "The Cloud Minders", and "All Our Yesterdays", and McCoy and Scott found love in "For the World is Hollow and I Have Touched the Sky" and "The Lights of Zetar", respectively.
Of the junior crewmembers, Chekov had significant roles in "Spectre of the Gun" and "The Way to Eden", the latter giving a rare insight into his past. Sulu was given a chance to command the ship in "Spock's Brain", for the first time since "Errand of Mercy", and accompanied Kirk and McCoy on an away team in "That Which Survives", while Uhura and Christine Chapel finally had an opportunity to get closer to the two leads in "Plato's Stepchildren", albeit at the behest of telekinetic aliens.
The Klingons made two major appearances in "Elaan of Troyius" and "Day of the Dove". The latter introduced the character of Kang, who was later seen in Star Trek: Deep Space Nine and Star Trek: Voyager. The Romulans appeared in person for the first time since "Balance of Terror" when they returned in "The Enterprise Incident", and the Tholians were introduced in "The Tholian Web". "The Savage Curtain" saw Kirk and Spock forced to play out the battle against good and evil, with three of the other participants, Phillip Green, Kahless the Unforgettable, and Surak, reappearing in later series as their original selves. The episode also marked the last appearance of Uhura on the show.
- James Doohan as Montgomery Scott
- George Takei as Hikaru Sulu
- Nichelle Nichols as Uhura
- Walter Koenig as Pavel Chekov
- Majel Barrett as Christine Chapel
- Eddie Paskey as Leslie
- Fred Freiberger – Producer
- Robert H. Justman – Co-Producer ("Spectre of the Gun" – "That Which Survives")
- Gene Roddenberry – Executive Producer
- Gregg Peters – Associate Producer
- Edward K. Milkis – Associate Producer
- Douglas S. Cramer – Executive in Charge of Production
- Gregg Peters – Unit Production Manager
- Arthur H. Singer – Story Consultant
- Walter M. Jefferies – Art Director
- John Dwyer – Set Decorator
- Jerry Finnerman – Director of photography ("Spectre of the Gun" – "The Empath")
- Al Francis – Director of photography ("The Tholian Web" – "Turnabout Intruder")
- Gil Kissel – Assistant Director
- Claude Binyon, Jr. – Assistant Director
- Gene DeRuelle – Assistant Director
- Bill Brame – Film Editor
- Donald R. Rode – Film Editor
- William Ware Theiss – Costume Designer
- Fred B. Phillips – Make-Up Artist
- Pat Westmore – Hair Stylist
- George A. Rutter – Script Supervisor
- Joseph D'Agosta – Casting Director
- William J. Kenney – Casting Director
- Irving A. Feinberg – Property Master
- Jim Rugg – Special Effects
- Douglas H. Grindstaff – Sound Effects Editor
- Richard Lapham – Music Editor
- Gordon L. Day – Re-recording Mixer
- Carl W. Daniels – Production Mixer
- George H. Merhoff – Gaffer
- George Rader – Head Grip
- Larry Abbott – Makeup artist ("The Way to Eden")
- George Barr – Makeup artist ("The Way to Eden")
- Kellam de Forest – Research
- John Finger – Director of Photography ("Requiem for Methuselah")
- Al Francis – Camera Operator ("Spectre of the Gun" – "The Empath")
- Ernest Haller – Director of Photography ("Requiem for Methuselah")
- Al Jacoby – Assistant Property Master
- Mike May – Props
- Bill McGovern – Clapper/Loader
- Mike Minor – Additional designs ("The Tholian Web")
- Tiger Shapiro – Second Assistant Director
- Charles Washburn – Second Assistant Director
- Andrea Weaver – Women's Costumer
- Jud Taylor
- Some production staff members were disappointed with season three. In a 2006 interview, Leonard Nimoy called it "very weak in general, but it was especially not good for Spock." 
- Ira Steven Behr once said that both he and his sister were disappointed with this third season. He also commented that his disappointment with the season was similar to the reaction of "most fans." (AOL chat, 1997)
- For the third season, the title and credits were in a light blue color, much like the credits of Star Trek: The Next Generation.
- Kirk no longer wore a green wrap-around shirt in any of the episodes, though officers were seen wearing the full dress uniform in "Is There in Truth No Beauty?" and "The Savage Curtain". Also in the third season, Scott's dress uniform was accompanied by a traditional Scottish kilt. The uniforms were no longer made of velour (which shrank every time it was cleaned), but of double-knit polyester.
- Each episode of the third season now cost about US$175,000, the budget having been reduced even further, while the salaries of the main cast increased. Consequently, only two episodes out of the twenty-four this season ("The Paradise Syndrome" and "All Our Yesterdays") featured location scenery.
- Gene Roddenberry was initially promised an early evening time slot (Mondays at 7:30 pm) by NBC. However, this would have required their top-rated series Laugh-In to be moved from its 8 pm time slot to 8:30. Laugh-In Producer George Schaltter threatened to take his show to another network unless it was guaranteed the 8 pm slot. NBC capitulated, forcing Star Trek to air its third season in the only remaining slot on the schedule – Fridays at 10 pm. Roddenberry threatened to leave Star Trek entirely if it wasn't put back to the promised time slot, but NBC rejected his threats due to the show's low ratings. He technically kept the post of executive producer for this season, but had actually left for MGM to work on other projects.
- Because of Roddenberry's withdrawal, scripts were no longer revised or re-written by him, nor by either Gene L. Coon or D.C. Fontana, who both left the series earlier. Script quality greatly suffered because of this. (Inside Star Trek: The Real Story)
- After Roddenberry and most of the writing staff left after the second season, Fred Freiberger took over as producer, with Arthur Singer replacing D.C. Fontana as script consultant. According to Fontana, Singer came to the set one day, and asked, "By the way, what does that transporter thing do again?" 
- Robert Justman was promoted to co-producer, but left the series after "Let That Be Your Last Battlefield". Gregg Peters became the new associate producer.
- A most important change was the departure of cinematographer Jerry Finnerman after "The Empath", and his replacement with his former camera operator, Al Francis, which affected the visual style of the series.
- Several new writers were brought in. Many of them were non-professionals, who sent in story outlines, which were read and recommended by Justman. These included Jean Lisette Aroeste, Joyce Muskat, and Judy Burns.
- According to Star Trek Lives! writer Joan Winston, NBC passed on an option for two additional episodes (a twenty-fifth and twenty-sixth) for the third season. William Shatner would have directed the twenty-fifth episode, "The Joy Machine". Ultimately, it was another two decades before Shatner got the opportunity to direct a Star Trek production (the film Star Trek V: The Final Frontier, which was released almost twenty years to the day after TOS series finale "Turnabout Intruder") and twenty-one years before a Star Trek episode would be directed by a member of the cast (TNG: "The Offspring", directed by Jonathan Frakes).
| Previous Season:|
TOS Season 2
| Seasons of|
Star Trek: The Original Series
|Final season in series|