Suspension of disbelief is the avoidance—often described as willing—of critical thinking and logic in understanding something that is unreal or impossible in reality, such as something in a work of speculative fiction, in order to believe it for the sake of enjoying its narrative. Historically, the concept originates in the Greco-Roman principles of theatre, wherein the audience ignores the unreality of fiction to experience catharsis from the actions and experiences of characters.

The phrase was coined and elaborated upon by the English poet and philosopher Samuel Taylor Coleridge in his 1817 work Biographia Literaria: "that willing suspension of disbelief for the moment, which constitutes poetic faith".

The phrase first appeared in English poet and aesthetic philosopher Samuel Taylor Coleridge's Biographia Literaria, where he suggested that if an author could infuse a "human interest and a semblance of truth" into a story with implausible elements, the reader would willingly suspend judgement concerning the implausibility of the narrative. Coleridge was interested in returning fantastic elements to poetry and developed the concept to support how a modern, enlightened audience would continue to enjoy such types of literature. Coleridge observed that his work, such as his contributions to the Lyrical Ballads, his collaboration with William Wordsworth, essentially involved attempting to explain supernatural characters and events in plausible terms so that implausible characters and events of the imagination can seem to be truthful and present a greater contrast between fiction and reality. Coleridge also referred to this concept as "poetic faith", citing the concept as a feeling analogous to the supernatural, which stimulates the mind's faculties regardless of the irrationality of what is being understood.

Coleridge recalled:

It was agreed, that my endeavours should be directed to persons and characters supernatural, or at least romantic, yet so as to transfer from our inward nature a human interest and a semblance of truth sufficient to procure for these shadows of imagination that willing suspension of disbelief for the moment, which constitutes poetic faith. Mr. Wordsworth on the other hand was to propose to himself as his object, to give the charm of novelty to things of every day, and to excite a feeling analogous to the supernatural, by awakening the mind's attention from the lethargy of custom, and directing it to the loveliness and the wonders of the world before us.

This concept had previously been understood in antiquity, particularly in the Roman theoretical concerns of Horace and Cicero who wrote in a time of increasing skepticism about the supernatural. In Horace's Ars Poetica, he used the quotation Ut pictura poesis, meaning "as is painting so is poetry". According to David Chandler, Coleridge also originally drew his notion from Johann Jakob Brucker's Historia Critica Philosophiae which cited the phrase "assensus suspensione" ("suspension of assent"); Brucker's phrase was itself a modernization of the phrase "adsensionis retentio" ("a holding back of assent") used by Cicero in his Academica.

The traditional concept of the suspension of disbelief as proposed by Coleridge has been claimed - despite Coleridge's own statement quoted above - to be not about suspending disbelief in the reality of fictional characters or events, but the suspension of disbelief in phenomena that are regarded as implausible. This can be demonstrated in the way a reader suspends disbelief in supernatural phenomena themselves — simulating the feelings of a character that is experiencing the phenomena in the narrative of a story—rather than simply the implausibility of the phenomena in a story.

The phrase "suspension of disbelief" came to be used more loosely in the later 20th century, often used to imply that the burden was on the reader, rather than the writer, to achieve it. This might be used to refer to the willingness of the audience to overlook the limitations of a medium, so that these do not interfere with the acceptance of those premises. These premises may also lend to the engagement of the mind and perhaps proposition of thoughts, ideas, art and theories. With a film, for instance, the viewer has to ignore the reality that they are viewing a staged performance and temporarily accept it as their reality in order to be entertained. Early black-and-white films are an example of visual media that require the audience to suspend their disbelief for this reason. Cognitive estrangement in fiction involves using a person's ignorance to promote suspension of disbelief.