Much of the worldbuilding in this book has appeared in other E.T. media, such as the Universal Studios attraction E.T. Adventure and several video games.
E.T.: The Book of the Green Planet provides examples of:
- Astral Projection: E.T. has the ability to watch what's happening to Elliott back on Earth by sending an invisible miniature projection of himself through space.
- Bar Full of Aliens: The Micro Tech Club not only has the titular Micro Techs, but Flopglopples and various sentient plants helping to run the place.
- Bizarre Instrument: Various plants grown on the Green Planet are used as musical instruments, such as a band in the Micro Tech Club: Fluteroots are the wind instruments, Timpanums are the drums, and Trompayds are the trumpets.
- Brought Down to Normal: The novel retcons the movie by saying that E.T. only discovered his power of telekinesis when he was on Earth, and after he returns to the Green Planet he loses that ability.
- Cosmic Egg: Mentioned throughout the story, as a Cosmic Egg appears to be part of a creation myth for E.T.'s species.
- Crapsaccharine World: The Green Planet may be a beautiful, whimsical world inhabited by cute aliens and intelligent plants, but it's ruled by a government that ranges from being obstructive bureaucrats to a totalitarian state in its efforts to keep E.T. down and prevent him from going back to Earth — not so different from the FBI agents who hunted him on Earth, really. Because E.T.'s people don't care about anything other than plants, the book seems to imply that the government is run by computers.
- Everyone Calls Him "Barkeep": The protagonist is always referred to as "E.T." in the narration, but his real name is never revealed — members of his own species only ever call him "a Doctor of Botany".
- I Have Many Names: The Green Planet is also known as Alata Zerka, Brodo Asogi, Od-Di-Pa 5, Tum Lux O-ty, and Vomestra, all of which are said to translate to "green planet". When Star Wars Legends began including E.T. easter eggs, Brodo Asogi was used as the primary term for the planet, even down to the name of the species itself ("Asogians").
- Klingons Love Shakespeare: Following his experiences on Earth, E.T. can't stop talking about human culture. He recites lyrics from "rocking and rolling" music, and thinks a "Baa Sket Ba" (basketball) is a living being.
- Mentor Archetype: Botanicus guides E.T.'s role as a botanist and helps him on his overall journey.
- My Species Doth Protest Too Much:
- E.T.'s experience on Earth has turned him into a Cultural Rebel, willing to defy his government's orders to reunite with Elliott.
- Unlike other Micro Techs, Micron wants to be a musician instead of an engineer.
- Organic Technology: After several failed attempts at going back to Earth that land him in trouble with the authorities, E.T. and his friends eventually build a spaceship almost entirely out of plants. Its hull is a giant turnip, and various alien plants are used to provide lighting, life support and propulsion.
- Planet of Hats: Apparently, just about every member of E.T.'s species is a botanist, and every Micro Tech is an engineer.
- Reassigned to Antarctica: To punish E.T. for getting stranded on Earth, the Green Planet's government reassigns him to a dead-end job on a small farm in his home village.
- Rubber Man: Flopglopples are sort of like talking ferrets, but they have a long snake-like body and forelimbs that can stretch to great distances, and three hind legs that allow them to run at Super-Speed.
- Sequel Hook: Having spent the entire book trying to get back to Elliott, E.T. finally makes it offworld at the end, but the story of his reunion with Elliott is saved for a sequel that was never written. The closest thing resembling a sequel is the Christmas 2019 Comcast/Sky TV commercial where he visits 48-year-old Elliott and his family. If both the commercial and this novel are canon,
Fridge Logic makes you wonder why it took so long, or whether E.T. and Elliott had a previous reunion that was never depicted. - Smarter Than You Look: Flopglopples are seen as just silly creatures In-Universe, but are much more intelligent and thoughtful than they initially seem.
- Time Dilation: When E.T. is rescued from Earth, the 3 million light year trip back to the Green Planet is almost instantaneous to the occupants of the ship, but a few years have passed on Earth so that in this novel's storyline, Elliott is about 12 or 13 years old. (This is a heavily Downplayed Trope because the way relativity is supposed to work, if you traveled 3 million light years at close enough to the speed of light for your journey to seem almost instantaneous aboard your ship, the trip would still take over 3 million years as seen from the outside.)
- Treants: Jumpums are giant trees that, as their name suggests, jump around.
- Truly Single Parent: E.T. has only one parent, whom he literally addresses as "Parent". It's implied that all of his species reproduce asexually and may be hermaphrodites. Although the narration uses he/him pronouns for E.T., his Parent is always referred to as "it".
- You Can't Go Home Again: After spending all of the film trying to get back home E.T. finds that he now misses Earth, and especially Elliott, more than ever.
