An unreliable narrator is a narrator whose credibility is compromised. They can be found in fiction and film, and range from children to mature characters. The term was coined in 1961 by Wayne C. Booth in The Rhetoric of Fiction. While unreliable narrators are almost by definition first-person narrators, arguments have been made for the existence of unreliable second- and third-person narrators, especially within the context of film and television, and sometimes also in literature.

Sometimes the narrator's unreliability is made immediately evident. For instance, a story may open with the narrator making a plainly false or delusional claim or admitting to being severely mentally ill, or the story itself may have a frame in which the narrator appears as a character, with clues to the character's unreliability. A more dramatic use of the device delays the revelation until near the story's end. In some cases, the reader discovers that in the foregoing narrative, the narrator had concealed or greatly misrepresented vital pieces of information. Such a twist ending forces readers to reconsider their point of view and experience of the story. In some cases the narrator's unreliability is never fully revealed but only hinted at, leaving readers to wonder how much the narrator should be trusted and how the story should be interpreted.