Mobius is the planet that the Sonic the Hedgehog characters are from in the comic book series made by Archie Comics (United States) and Fleetway Comics (Europe), and in all three American cartoons, including the light-hearted Adventures of Sonic the Hedgehog, the more serious ABC cartoon Sonic the Hedgehog (considered as "SatAM" by the Sonic community), and Sonic Underground.

In the Japanese versions of the game, the planet on which the action took place was Earth, renamed for some unspecified reason in the English-language versions so that it was another planet entirely, which was an idea that was, until the Western release of Sonic Adventure games, adopted as the canon for the Western fiction.

Depictions of the planet vary from universe to universe, with the most basic being from the UK fiction (Sonic the Comic and several books)—that it is simply another planet. In SatAM, it is never particularly specified; in Archie, however, Mobius is eventually revealed to be a future iteration of Earth, but consists of Mobians (animalistic beings) and is ruled by a dictator, Dr. Robotnik, who orginally went by the name of Julian Kintobor before he became a dictator trying to destroy all Mobian life, and trying to turn them into Robots (considered as "Robians") via roboticization (presumably, this retcon of Mobius into a future Earth is in some measure a result of the Western games' decision to do away with Mobius and present it as Earth). In fact, the comics have stated that Mobius exists in an enirely different universe from our own that can be reached through the Cosmic Interstate, an intergalactic road that connects different universes and realities across time and space. In "Sonic Underground," an alternate take on the SatAM universe, no reference to Earth is made (nor is Robotnik's first name particularly mentioned) although the planet appears to be surrounded by either neighboring planets or moons (it is never specified which), suggesting, perhaps, that Mobius is an alien world. In Adventures of Sonic the Hedgehog, the place is completely free, with Dr. Ivo Robotnik just trying time and again to take it over (and usually failing miserably).

Outside of of Sonic Spinball and Dr. Robotnik's Mean Bean Machine, which were made to promote the cartoons, the Sonic video games are not intended to take place on Mobius, but instead on Earth. This is proven by the more recent Sonic games, which have clearly placed the action on Earth, featuring much human interaction, which leaves the original western notion of Mobius somewhat disrupted. Most people have dropped the term entirely when speaking about the games in general, with the aforementioned exceptions.

The newest Sonic cartoon (an anime), Sonic X, apparently attempts to tie these two aspects together in some way, as, while the majority of its action takes place on Earth, Sonic and co. are transported there from another planet, and return there at the series end. It is clearly presented as their home world, leading some to theorize/believe, fairly logically, that this planet is Mobius. The planet is not referred to by name, so there's really nothing to say that it is Mobius, but at the same time, there is nothing disprove the notion either, besides the circumstantial fact that there has been virtually no mention of Mobius in Japan, leading many people do not believe it is intended to be that way.

Mobius is also been the home of Sonic in many fanfiction stories, fanart pieces, fangames, and in Sonic based role play.