A lost film is a feature or short film that is no longer known to exist in any studio archives, private collections, or public archives such as the Library of Congress.

Conditions

During most of the 20th century, U.S. copyright law required at least one copy of every American film to be deposited at the Library of Congress at the time of copyright registration, but the Librarian of Congress was not required to retain those copies: "Under the provisions of the act of March 4, 1909, authority is granted for the return to the claimant of copyright of such copyright deposits as are not required by the Library." Of American silent films, far more have been lost than have survived, and of American sound films made from 1927 to 1950, perhaps half have been lost. The phrase "lost film" can also be used in a literal sense for instances where footage of deleted scenes, unedited, and alternative versions of feature films are known to have been created but can no longer be accounted for. Sometimes a copy of a lost film is rediscovered. A film that has not been recovered in its entirety is called a partially lost film. For example, the 1922 film Sherlock Holmes was eventually discovered but some of the footage is still missing.

For this list of lost films, a lost film is defined as one of which no part of a print is known to have survived. For films in which any portion of the footage remains (including trailers), see List of incomplete or partially lost films.

Films may go missing for a number of reasons. One major contributing factor is the common use of nitrate film until the early 1950s. This type of film is highly flammable, and there have been several devastating fires, such as the 1937 Fox vault fire, the 1967 MGM vault fire, and the Universal Pictures fire in 1924. Black-and-white film prints judged to be otherwise worthless were sometimes incinerated to salvage the meager scrap value of the silver image particles in their emulsions. Films have disappeared when production companies went bankrupt. Occasionally, a studio would remake a film and destroy the earlier version. Silent films in particular were once seen as having no further commercial value and were simply junked to clear out expensive storage space.