Adaptation

An adaptation is the transformation of a source text into another medium. The most common kind of adaptation is from print into audio-visual text, like movie adaptations of novels. However, adaptations span media—from musical adaptations of popular anime to movie reworkings of video games, anything goes.
==Movie Adaptations of Novels==
It has been noted, e.g. in the Harry Potter fandom and Twilight fandom, that adaptations draw in new fans, who may be enticed by familiar or attractive actors, or may relate better to a visual experience than a written one. Another notable example is the 2020 Netflix feature Enola Holmes, whose release caused a sharp uptick in traffic for the small body of fanworks on AO3 derived from the Nancy Springer books on which the film was based.
In some fandoms, film adaptations are considered so similar to their print sources or so dependent on them that it is rare in those fandoms to distinguish between fans of the print source and fans of the film. When print and film versions of a story differ in some details, there is often debate over whether details from the film version should be considered canon, especially when they contradict the original print version. Separate fandoms may develop, often with some conflict between "bookverse" and "movieverse" fans.
TV series based on books have also become increasingly popular. Examples include The Dresden Files, Dexter and True Blood. The TV adaptations are often very different from the original sources.
==Movie Adaptations of Comics==
Filmmakers have been adapting characters and stories from comics since early in cinematic history. Saturday afternoon movie serials featured heroes such as Flash Gordon and Mandrake the Magician from newspaper strips, as well as Batman and Superman from comic books. These early adaptations typically featured episodic stories similar in structure to the printed material they emulated. 
This changed in 1978, with the big-screen release of Superman starring Christopher Reeve in the title role. The film presented a full-fledged origin story for its title character, condensing and reworking material from decades of comics continuity, and set a new standard for comics adaptations. The origin story became the default big-screen superhero plot for the next several decades, with examples ranging from 1978's Batman to The Rocketeer in 1991 and Iron Man in 2008. Many of these movies developed their own fandoms, distinct from those devoted to their counterparts in the print comics, though a degree of overlap is not uncommon; e.g. X-Men comics and X-Men Movieverse.
The debut of Iron Man shifted the genre again, spawning the Marvel Cinematic Universe. The resulting franchise has been both a record-breaking commercial success and the catalyst for a large and active fandom, with thousands of fanworks represented on AO3. MCU films have drawn on and re-imagined comics canon in a variety of ways, and opened the way for superhero films to tell more kinds of stories; Ant-Man has been referred to as a "heist picture", while Captain America: The Winter Soldier has been characterized as a spy thriller.
==Television Adaptations of Comics==
Comics characters, particularly (but not exclusively) superheroes, have also been staples of both live-action and animated TV adaptations. Marvel and DC Comics heroes were a constant presence in Saturday morning and weekday afternoon cartoons from the 1960s through the 1990s. The 1960s and '70s Saturday series featured short, free-standing episodes with extremely simple plots, closely replicating the form of a one-shot comic book story. In the 1990s, however, the paradigm changed; series from Marvel starring Spider-Man and the X-Men introduced multi-part story arcs and crossover appearances adapting popular storylines from the print comics, and DC's Batman: The Animated Series spawned a host of spinoffs and related projects that evolved into the DCAU (sometimes referred to as the "Timmverse", in recognition of Bruce Timm, producer and architect of many of the relevant shows). The DCAU in particular has developed and retained a sizeable fandom, to the extent that DCAU versions of many of DC's iconic characters may now be more widely recognized than their print-media (or even feature film) counterparts.
Live-action series derived from comics have also been popular. The 1966 Batman series starring Adam West remains a cult favorite, though fanworks derived from the show are relatively scarce. By contrast, Lois and Clark, starring Dean Cain and Teri Hatcher, generated a moderate fan following in its time, and Smallville sparked a sizeable ongoing fandom.
Not all TV comics adaptations are superhero shows, however. Sabrina the Teenage Witch, starring Melissa Joan Hart, was a successful situation comedy derived from the Archie Comics character. More recently, Riverdale has re-imagined the main cast of the Archie comics in a soap opera format. Both have generated modest fandom activity.
==Adaptations of Manga==
Many anime series are adaptations of manga. Sometimes the adaptations are very close to the originals, but some are extremely different. Often an anime starts running soon after the manga gains popularity and thus will soon run out of material to animate.
Once that happens there are two possible choices. The first is to stop the main arc and insert a filler arc, eventually returning to the main story once more manga chapters have been published (this is common with shounen series such as Bleach and Naruto). The other method is to continue on and make up material, possibly with some vague input from the creator of the manga. This usually results in a vastly different story, due to the fact that the anime writers could not predict plot twists for the manga. Fullmetal Alchemist is an example of this type of adaptation; the anime and manga are different in more ways than they are similar.
Another choice is to do a limited-run anime (either one season of 13 episodes, or a direct-to-video series or film) covering only the beginning of the story. Angel Sanctuary is an example of a popular manga whose anime only covers a small part of the series.
Manga are also often adapted to live-action TV series. Because Japanese shows run for a fixed length (10-13 episodes), these adaptations are usually very different from the manga they were based on.