A plot twist is a literary technique that introduces a radical change in the direction or expected outcome of the plot in a work of fiction. When it happens near the end of a story, it is known as a twist ending or surprise ending. It may change the audience's perception of the preceding events, or introduce a new conflict that places it in a different context. A plot twist may be foreshadowed, to prepare the audience to accept it, but it usually comes with some element of surprise. There are various methods used to execute a plot twist, such as withholding information from the audience, or misleading them with ambiguous or false information. Not every plot has a twist, but some have multiple lesser ones, and some are defined by a single major twist.

Since the effectiveness of a plot twist usually relies on the audience's not having expected it, revealing a plot twist to readers or viewers in advance is commonly regarded as a spoiler. Even revealing the fact that a work contains plot twists – especially at the ending – can also be controversial, as it changes the audience's expectations. However, at least one study suggests that this does not affect the enjoyment of a work.

Many television series, especially in crime fiction, use plot twists as a theme in every episode and some base their whole premise on the twist; for example, The Twilight Zone and Tales of the Unexpected.^{[citation needed]}

An early example of the romance genre with multiple twists was the Arabian Nights tale "The Three Apples". It begins with a fisherman discovering a locked chest. The first twist occurs when the chest is broken open and a corpse is found inside. The initial search for the murderer fails, and a twist occurs when two men appear, separately claiming to be the murderer. A complex chain of events finally reveals the murderer to be the investigator's own slave.

Literary analysts have identified several common categories of plot twists, based on how they are executed.

Anagnorisis, or discovery, is the protagonist's sudden recognition of his or her own or another character's true identity or nature. Through this technique, previously unforeseen character information is revealed. A notable example of anagnorisis occurs in Oedipus Rex: Oedipus kills his father and marries his mother in ignorance, learning the truth only toward the climax of the play. The earliest use of this device as a twist ending in a murder mystery was in "The Three Apples", a medieval Arabian Nights tale, where the protagonist Ja'far ibn Yahya discovers by chance a key item towards the end of the story that reveals the culprit behind the murder to have been his own slave all along.

Flashback, or analepsis, a sudden, vivid reversion to a past event, surprises the reader with previously unknown information that solves a mystery, places a character in a different light, or reveals the reason for a previously inexplicable action. The Alfred Hitchcock film Marnie employed this type of surprise ending. Sometimes this is combined with the above category, as the flashback may reveal the true identity of one of the characters, or that the protagonist is related to one of the villain's past victims, as Sergio Leone did with Charles Bronson's character in Once Upon a Time in the West or Frederick Forsyth's The Odessa File.

A cliffhanger, or cliffhanger ending, is a plot device in fiction which features a main character in a precarious or difficult dilemma or confronted with a shocking revelation at the end of an episode of serialized fiction. A cliffhanger is hoped to incentivize the audience to return to see how the characters resolve the dilemma. A notable example is in the 1980 Star Wars film The Empire Strikes Back: protagonist Luke Skywalker, who was told by Obi-Wan Kenobi in the previous film that the antagonist Darth Vader had killed his father, is told by Vader that he is Luke’s father.