Reboot means to discard all previous continuity in the series and start anew. Effectively, all previously-known history is declared by the writer to be null and void and the series starts over from the beginning. This differs from a creator producing a separate adaptation of another creator's work in an alternate reality and instead requires that the rebooted continuity supersede the older continuity as the new official version.
This term is often applied to comic books, where the prevailing continuity can be very important to the progress of future installments, acting (depending on circumstances and one's point of view) as a rich foundation from which to develop characters and storylines, or as a box limiting the story options available to tell and an irreconcilable mess of contradictory history. Such large continuities also become a barrier to introducing newcomers to the fandom, as the complex histories are difficult to learn, and make understanding the story very difficult; a reboot would theoretically give the chance for new fans to experience the story by reintroducing it in smaller and easier to understand installments; however, this has never "officially" happened in Marvel Comics, although there are several instances where it was attempted, and the new continuity was instead later relegated to alternate realities.
- In the mid-1990s, Marvel turned several of their titles over to studios affiliated with Image Comics, and these titles (Fantastic Four, Captain America, the Avengers, and Iron Man — the Hulk would be included in this trend only as a character, but without his own title) were adapted in a new continuity; meanwhile, the rest of Marvel's line maintained the original continuity in which the affected characters were presumed to have died in a cataclysmic battle. The new titles lasted only a year, at which point the heroes involved returned to the original universe and the perceived rebooted continuity was integrated into the original continuity. (See Heroes Reborn.)
- In addition, Marvel Comics also published Spider-Man: Chapter One by John Byrne, which was meant to be a complete reboot to the Spider-Man series and was treated as such until editorial changes relegated the series to alternate universe status, making all potential changes the original continuity null and void.
- In 2000, Marvel launched the Ultimate Marvel line of comic books that adapted the Marvel Universe. The Ultimate series was intended to modernize the characters, to rewrite the individual characters into a more cohesive universe, and to make the series more appealing to non-Marvel fans; the huge back-story of the Marvel Universe, made it very difficult for newcomers to understand the characters and storylines. Unlike most reboots; however, the original Marvel Universe continued to publish as well. This ensured the two continuities existed as parallel universes rather than a true reboot.
- Between 2003-2005, Marvel ran Supreme Power, a modernization of Squadron Supreme, which like the Ultimate Marvel line, ran concurrently with the original continuity in another alternate Universe instead of replacing the existing line.