A dream sequence is a technique used in storytelling, particularly in television and film, to set apart a brief interlude from the main story. The interlude may consist of a flashback, a flash-forward, a fantasy, a vision, a dream, or some other element.

Commonly, dream sequences appear in many films to shed light on the psychical process of the dreaming character. For instance in Pee-Wee's Big Adventure, the purpose of Pee Wee's dreams is to inform the audience of his anxieties and fears after losing his bike ^[1]. Other times major action takes place in dreams, allowing the filmmaker to explore infinite possibilities, as Michel Gondry demonstrates in The Science of Sleep. Harvard psychologist Deirdre Barrett points out in the film chapter of The Committee of Sleep that, while the main content of dream sequences is determined by the film's overall plot, visual details often reflect the individual dream experience of the screenwriter or director. For Hitchcock’s Spellbound, Dali designed sharply angled sets inspired by his own dream space. Ingmar Bergman lit dream sequences in several films with a harsh glare of light which he says reflects his own nightmares (though most people’s have dim light), and Orson Welles designed a scene of the trial to reflect the manner in which architecture constantly changed in his dreams ^[2]. Films normally present dreams as a visually accessible or objectively observed space, a discrete environment in which characters exist and interact as they do in the world rather than restricting themselves to the subjective point of view a dream is normally experienced from in real life ^[3].

Audio or visual elements, such as distinctive music or coloration, are frequently used to signify the beginning and end of a dream sequence in film. It has also become commonplace to distinguish a dream sequence from the rest of the film by showing a shot of a person in bed sleeping or about to go to sleep. Other films show a dream sequence followed by a character waking up in their own bed, such as the dream sequence George Gershwin composed for his film score to Delicious. In classic Hollywood, the wavy dissolve was the standard way to transition between reality and a dream; there would be a close-up of the character having the dream, which would begin shimmering as we crossed over from reality to fantasy ^[4]. One of the most common contemporary transitions into a fantasy is to zoom in on a character’s face and then spin around to the back of that character to reveal that he/she is now standing in an alternate reality ^[5]. Perhaps, the most common technique today is the post-reveal in which a character is shown in an awkward or unusual situation, the scene builds to an even more absurd or bizarre situation, and then suddenly we cut to the character waking up ^[6] as exemplified by the opening sequence of Bring It On where a pep rally with irreverent routines builds into a bizarre moment where Terrence is revealed topless and then her character wakes up and the dream sequence is revealed ^[7]. This is akin to the technique wherein a dream sequence is a plot device in which an entire story has been revealed to be a dream. As opposed to a segment of an otherwise real scenario, in these cases it is revealed that everything depicted was unreal. Often this is used to explain away inexplicable events. Because it has been done, in many occasions, to resolve a storyline that seemed out of place or unexpected, it is often considered weak storytelling; and further, in-jokes are often made in writing (particularly television scripts) that refer to the disappointment a viewer might feel in finding out everything they've watched was a dream. For example, entire sequences of the Family Guy episode "Stewie Kills Lois and Lois Kills Stewie" are revealed to have taken place within a virtual reality simulation, upon which a character asks whether a potential viewer could be angry that they've effectively watched a dream sequence. The TV show Dallas revealed that an entire season of the program was a dream. This technique can also be effective and its use lauded when the status of dream or reality is left more ambiguous as it was in The Wizard of Oz ^[8].

The dream sequence that Atossa narrates near the beginning of Aeschylus' Athenian tragedy The Persians (472 BCE) may be the first in the history of European theatre ^[9]. The first dream sequence in a film is more contested ^[10]. Film critic, Bob Mondello, says that the first famous movie with a dream sequence was Buster Keaton’s Sherlock, Jr. (1942) ^[11], but James Walter notes G.A. Smith’s use of a dream sequence in Let Me Dream Again (1900) ^[12], and Leslie Halpern claims that the earliest dream sequence was in Edwin S. Porter’s The Life of an American Fireman (1903) ^[13].