According to James Doohan (Scotty), this was the only episode of the series that he did not like.

Skip Homeier (Dr. Severin) previously played Deputy Führer Melakon in "Patterns of Force".

Charles Napier and Deborah Downey composed several of their own songs for the episode, working with Arthur Heinemann, the episode writer. The music was recycled a year later for the movie The Hanging of Jake Ellis, which Napier and Downey starred in and sang.

Joanna McCoy, Dr. McCoy's daughter, was originally to appear. The script, titled "Joanna," was rejected.

Executive Vice President Douglas S. Cramer came up with the insult term of "Herbert." this may have been a reference to his predecessor, Herbert F. Solow.

Kirk: Are they aboard? Scotty, are they aboard?
Scotty: Aye, Captain. They are, and a nice lot too.

Spock: In addition, you've caused an interstellar incident which may have destroyed everything that's been negotiated between your planet and the Federation.
Tongo Rad: You've got a hard lip, Herbert.

Spock: But they've rejected all that and all that this technology provides. And they seek the primitive. There are many who are uncomfortable with what we have created. It is almost a biological rebellion, a profound revulsion against the planned communities, the programming, the sterilized, artfully balanced atmospheres. They hunger for an Eden, where Spring comes.
Kirk: All do. The cave is deep in our memory.
Spock: Yes, that is true, Captain.
Kirk: But, uh, we don't steal space cruisers and act like irresponsible children. What makes you so sympathetic toward them?
Spock: It is not, uh, sympathy so much as curiosity, Captain: a wish to understand. They regard themselves as aliens in their own worlds, a condition with which I am somewhat familiar.

Kirk: Spock. What does Herbert mean?
Spock: It is, um, um, somewhat, uh, uncomplimentary, Captain. Herbert was a minor official notorious for his rigid and limited patterns of thought.
Kirk: Well, I shall try to be less rigid in my thinking.

Adam: I'm gonna crack my knuckles and jump for joy, I got a clean bill of health from Dr. McCoy.

Scotty: Captain, I just had to give one of those barefooted whaddyacallems the boot out of here. He came into my engine room, bold as brass; tried to incite my crew to disaffect.

Adam: Hey, how about a session, you and us It would sound! That's what I came for. I wanted to ask, you know, great white captain upstairs, but he don't reach us. But, uh, would he shake on a session? I mean, we want to cooperate, like you ask, so I'm asking.
Spock: If I understand you correctly, I believe the answer might be "yes."

Scotty: I don't know why a young mind has to be undisciplined. They're troublemakers!
Kirk: I used to get into a little trouble when I was that age, Scotty, didn't you?

Kirk: The Romulans will view this as a military intrusion and attack. Bring the ship about now. If you bring her about and return to Star base, no charges will be leveled.
Adam: Like he said, Brother Sevrin.
Kirk: If you do not, you will never reach Eden. You and this ship will be destroyed.
Adam: He's got jelly in the belly. Real scared.

Kirk: We reach, Mr. Spock.

When Chapel collapses in Sickbay due to the sonic attack, the lights flicker although no other shots show this. The reason is that the footage is recycled from "Spock's Brain."

Twice in the episode, Kirk's part flips to his left, due to recycling footage. In both instances his ship's insignia can also be seen flipped. The first time is when Kirk emerges from Sickbay, the second time on Eden as he reacts to Sevrin running away.

Chekov's full name, Pavel Andreievich Chekov, is given here for the first time.

What Changed in the Remastered Version
General improvements cited on the main series page. The orbital shots of Eden get a surface upgrade, and two moons are seen in orbit. The hippies' stolen cruiser the Aurora receives a substantial upgrade and a totally different appearance, as well as a new explosion effect. The establishing landscape shot Eden when the landing party arrives now features an expanse of forests and mountains, with the moons visible in the sky.