- The USS Enterprise makes first contact with androids from the Andromeda Galaxy. This is made difficult at first due to the interference of Harcourt Fenton Mudd. (TOS: "I, Mudd")
- The USS Enterprise visits Deep Space Station K-7. (TOS: "The Trouble with Tribbles")
- The United Federation of Planets hosts the Babel Conference, which eventually results in Coridan's admission to the Federation. (TOS: "Journey to Babel")
- Kirk oversees a landing party on Argus X in order to search for the dikironium cloud creature. This expedition is helped by Ensign Garrovick and security officers Bardoli and Swensen. (TOS: "Obsession")
- The USS Intrepid is destroyed and its entire crew of Vulcans killed, as well as the destruction of the Gamma 7A system, by an enormous space going single-celled organism. (TOS: "The Immunity Syndrome")
- Kirk invents Fizzbin. (TOS: "A Piece of the Action")
- The USS Enterprise makes first contact with intergalactic beings the Kelvans from the Andromeda Galaxy. This first contact is at first difficult as the Kelvans attempt to hijack the Enterprise and kill one of the crew. (TOS: "By Any Other Name")
- Lieutenant Commander and Dr. Ann Mulhall joins the crew of the USS Enterprise. An astrobiologist, Ann Mulhall is the highest ranking female officer to serve aboard the Enterprise during its original five-year mission. (TOS: "Return to Tomorrow")
- Federation cultural observer and former history teacher of Captain James T. Kirk, John Gill, is shot and killed on the planet Ekos by Melakon after Gill denounces his own idea of a Nazi regime set up on Ekos as well as their battle against the Zeon and the subjugation and extermination of Zeon's population on a star system wide television broadcast. Melakon is in turn shot and killed by Isak. Thereafter, Isak and Ekosians Daras and Eneg agree to end the violence and set Ekos on a more humane path. (TOS: "Patterns of Force")
- Dr. Richard Daystrom suffers a mental breakdown aboard the USS Enterprise. (TOS: "The Ultimate Computer")
- The USS Enterprise makes first contact with the xenophobic Melkotians. (TOS: "Spectre of the Gun")
- The Dohlman of Elas named Elaan is married, in an arranged union, to the ruler of Troyius in the hopes of fostering peace between the planet Elas and the planet Troyius, which are both in the Tellun star system. (TOS: "Elaan of Troyius")
- The planet Amerind is saved from destruction by an asteroid by Kirk and Spock. (TOS: "The Paradise Syndrome")
- A brief alliance between the Klingon Empire and the Romulan Star Empire occurs. This results in an exchange of technology and spacecraft design, most notably the cloaking device to the Klingons. (TOS: "The Enterprise Incident")
- All the adults of the Starnes Expedition are killed, due to the alien Gorgan's influence on the children, on the Federation outpost planet Triacus. Gorgan is destroyed, a short time later, aboard the USS Enterprise. (TOS: "And the Children Shall Lead")
- The USS Enterprise makes first contact with the Eymorgs of Sigma Draconis VI after Kara steals Spock's brain to be used as the new Controller for that planet. McCoy puts Spock's brain back in Spock's head with the help of the Great Teacher, with the Eymorgs being forced to live, again, on the surface of that planet with the Morgs. (TOS: "Spock's Brain")
- One of the designers of the USS Enterprise and Federation engineer Dr. Larry Marvick dies a short time after looking at Medusan Ambassador Kollos. (TOS: "Is There in Truth No Beauty?")
- Dr. Miranda Jones boards a Medusan vessel to help ready Medusans to be navigators on Federation starships. (TOS: "Is There in Truth No Beauty?")
- Kirk, Commander Spock, and Doctor Leonard McCoy are able to save the mute native humanoid species of Gamma Vertis IV from the destruction of the star Minara going supernova by showing the Vian scientists Thann and Lal that Gem and her mute species can express love and compassion. (TOS: "The Empath")
- The star Minara supernovas. (TOS: "The Empath")
- The USS Defiant is discovered by the USS Enterprise adrift in the interphase of Tholian space with all of the crew dead due to mass insanity. After Kirk is rescued from the ship, unknown to the Federation and Starfleet, the USS Defiant, courtesy of a Tholian tri-cobalt warhead, ends up in the mirror universe in 2155 stolen by Commander Jonathan Archer and the crew of the ISS Enterprise. (TOS: "The Tholian Web"; ENT: "In a Mirror, Darkly")
- Dr. McCoy contracts the rare illness xenopolycythemia but is cured a short time later via the Fabrini's vast database. (TOS: "For the World is Hollow and I Have Touched the Sky")
- McCoy is briefly married to Natira. (TOS: "For the World is Hollow and I Have Touched the Sky")
- Kirk and Spock reprogram the Yonada's course to the one the Fabrini originally intended. (TOS: "For the World is Hollow and I Have Touched the Sky")
- Lokai steals a shuttlecraft from Starbase 4. (TOS: "Let That Be Your Last Battlefield")
- The planet Cheron's humanoid population destroys their cities and kills each other off in a civil war, making much of the planet uninhabitable to humanoid lifeforms; lower species animals encroach on and take over the cities. (TOS: "Let That Be Your Last Battlefield")
- Dr. McCoy, with the help of Lieutenant Brent and an operations division lieutenant, administers to the inmates/patients of Elba II asylum a revolutionary new medicine that potentially could eliminate mental illness. (TOS: "Whom Gods Destroy")
- Odona becomes patient zero (although she is cured of the disease herself) and introduces the disease Vegan choriomeningitis to her people on Gideon as a way to control the population on that planet. (TOS: "The Mark of Gideon")
- Ceti Alpha VI explodes and turns the former M class planet Ceti Alpha V into a barren wasteland. (Star Trek II: The Wrath of Khan)
- The Polaric Test Ban Treaty is signed after the near destruction of a Romulan research colony due to a polaric ion device explosion on Chaltok IV. (VOY: "Time and Again")
- Harry Mudd steals a spaceship to escape the androids from the Andromeda Galaxy. (TAS: "Mudd's Passion")
- A Slaver stasis box is discovered by archaeologists on the planet Kzin. (TAS: "The Slaver Weapon")
- The Keeper of the Shore Leave Planet dies. (TAS: "Once Upon a Planet")
- A Federation vessel makes first contact with the Children of Tama, but formal relations cannot be established due an inability to understand the Tamarian language, which is described as incomprehensible. (TNG: "Darmok")
- 2268 marks the start of the fourth year of Kirk's first five-year mission. (VOY: "Q2")
- On Sigma Draconis VI, the Congress of Morg and Eymorg is founded. (Star Trek: Star Charts (p. 34))
- Neural is made a protectorate of the Federation. (Star Trek: Star Charts, p. 34)
- "I, Mudd"
- "The Trouble with Tribbles"
- "Bread and Circuses"
- "Journey to Babel"
- "A Private Little War"
- "The Gamesters of Triskelion"
- "The Immunity Syndrome"
- "A Piece of the Action"
- "By Any Other Name"
- "Return to Tomorrow"
- "Patterns of Force"
- "The Ultimate Computer"
- "The Omega Glory"
- "Spectre of the Gun"
- "Elaan of Troyius"
- "The Paradise Syndrome"
- "The Enterprise Incident"
- "And the Children Shall Lead"
- "Spock's Brain"
- "Is There in Truth No Beauty?"
- "The Empath"
- "The Tholian Web"
- "For the World is Hollow and I Have Touched the Sky"
- "Day of the Dove"
- "Plato's Stepchildren"
- "Wink of an Eye"
- "That Which Survives"
- "Let That Be Your Last Battlefield"
- "Whom Gods Destroy"
- "The Mark of Gideon"
- "Trials and Tribble-ations" (in part)
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