All Fan Fic is arguably an Alternate Continuity, since the audience can assume it intends to follow Canon to a specific point, then branch off. Indeed, the only major fic types that don't branch off are post-series Continuation fics and those written to fit neatly into canon, as they don't disrupt the continuity. Because of this, fanfic authors labeling something an Alternate Universe Fic has a different implication, wherein a fundamental aspect of the series is completely overhauled from its point of origin.

The standards for how much is fundamental to the series vary by fandom and by time of writing, but the fic types that are usually considered AU are the following:

• Contextual Reassignment: When the fundamental aspect that is changed is the world itself. Overt changes in the universe rules and Worldbuilding constitute the most universally accepted meaning of AU. Thus, the fan equivalent to an Elseworld. However, there's a lot less tolerance of altering personalities and abilities. These come in two main forms:
  • Familiar Contextual Reassignment: When the characters are taken out of their world and placed in a setting that is fairly familiar to the author and readers — the High School AU is especially common, putting characters who would not have met or even existed for years in close proximity during teenage years.
  • Unfamiliar Contextual Reassignment: When the characters are taken out of their world and placed in a setting much more unfamiliar to the author or the reader — for example prison, a Nazi Death Camp, Normandy 1066, or possibly Mars. This is often called a Transplanted Character Fic. Historic examples are called Historical AUs.
• What If?: For lesser changes, there are the What Ifs about major events in the series — how 'major' counts as 'major' is debatable. There are three common forms of this.
  • Alternate History: Where the author takes one point of time, one event in the universe and changes the outcome of it radically, such as an important decision, or who won an important fight, and continues from that point. Sometimes called a Divergence Fic.
  • Character Facets: The author speculates on what would happen if a single facet of a character's environment was different about them, or may blatantly ignore a Word of God statement, for example, what if a character was blind, or had a little brother in the show right from the start.
  • Role Swap AU: The author explores how the story would change if two characters swap roles in the story. For example, if the unscrupulous Lancer becomes The Chosen One, while the original Stock Shōnen Hero is relegated to the role of their sidekick.
• Continuation: There are also the Continuation fics written before the series has finished, which are rendered AU when new episodes in canon contradict the events of the fic. This is more of an Alternate Continuity, as the opening paragraph mentions, but tends to be considered AU too. Retrospectively, these fics become the What If? variation mentioned above, but are written from a different stance. (Harry Potter ficdom was particularly prone to these until after the publication of Deathly Hallows.)

Full-blown AU fic is tricky, as it should require a fair notion of the original series itself, making it harder to read for some casual fans. There's also the major danger of the Transplanted Character Fic, because if you change the plot too much the story's not so much a Fan Fic as an original story with familiar names. On the plus side, rookie fans who might suffer from Continuity Lock-Out in the canon series because they only found it after it became established may be able to enjoy AU fics, particularly if they actually explain a lot of the universe and don't assume that you know all the important things already. Trying to follow Buffy the Vampire Slayer when you first start watching in its sixth season, with all the Character Development that's taken place up to that point, is a lot harder than cutting your teeth on an AU fic that starts out with the Scoobies in high school and doesn't require any advance knowledge of the setting.

See High School AU, Coffee Shop AU Fic, Magical Girl AU, Soulmate AU Fic, Super Fic and Modern AU Fic for particularly common variants. Contrast Elsewhere Fic and Pseudo-Canonical Fic. Some Fix Fic may take the form of this. See Universal-Adaptor Cast for when the work itself regularly does this. Other types, such as Crossover fics, are arguably AU too but don't get counted as such.

Categories with their own pages:

• Anime & Manga
• Video Games
• Western Animation

Examples: