Lost media is any media that is believed to have been forgotten or no longer exists in any format. The term primarily encompasses visual, audio, or audiovisual media such as films, television and radio broadcasts, music,^[2] and video games.^[3][4]

Many television and radio broadcast masters, recorded onto magnetic tape, may be lost due to the industry practice of wiping. Motion picture studios also often destroyed their original nitrate film elements, as film and broadcast material was often considered ephemeral and of little historical worth after they had made their revenue. Some media considered lost may exist in studio or public archives, but may not be available due to copyright or donor restriction rules. ^[5] Due to unstable nature of any format, film, tape, phonograph record, optical discs like CDs and DVDs, and digital data stored on hard drives, all naturally degrade over time, especially if not kept in correct storage conditions.

Preservation efforts attempt to avoid the loss of works; this is usually done by storing them in archives, one example being the Arctic World Archive, which has been the chosen location for the preservation of the code on public repositories on GitHub^[6] along with a wide range of data of interest to multiple companies, institutions and governments; including the Constitutions of Brazil and Norway.^[7]

A large portion of silent films made in the United States are now considered lost. A 2013 report made by the United States Library of Congress estimates that 70 percent of silent films made in the United States have been completely lost.^[8]

Lost television broadcasts are mostly those early television programs which cannot be accounted for in studio archives (or in personal archives); this is usually because of deliberate destruction or neglect.

Lostwave is an internet term used for songs with unknown authors or origin. Notable unknown songs include The Most Mysterious Song on the Internet,^[9] a 1980s new-wave song taped off a German radio broadcast, and Everyone Knows That (Ulterior Motives), a 17-second snippet of a lost song created in the 1980s or 1990s, recorded c. 1999.^[10]

Video games, including digital downloads, often fade from existence when digital game stores close, as demonstrated by the Wii Shop Channel, V Cast Network and the Nintendo eShop on the Wii U and Nintendo 3DS. The infamous P.T., a teaser to the unreleased Silent Hills game, became un-reloadable after its removal from the PlayStation Network within a year.^[11] The Wii U and Nintendo 3DS digital download games Dodge Club Party and Dodge Club Pocket were removed from Nintendo eShop in 2019 and 2022 and became publicly unavailable due to controlling issues.^[12]

According to the Video Game History Foundation, 87% of American video games released before 2010 are out of print and cannot be acquired outside of the grey market or piracy. Many of these titles are in danger of becoming lost, or already are.^[13]

Data stored in electronic computers risks being lost if it is not frequently migrated into more recent file formats. This happens because as new computer systems are developed and new technologies are built, now obsolete systems may break down over time, leaving the data inside inaccessible.^[14] Electronic data preservation is further complicated by the fact that unless an emulator for a given computer system which can decode the data is present at the time of the preservation, the original data may become inaccessible as the original hardware breaks down, as it may depend on the original hardware to be decoded,^[15] although in some cases the original data may be recoverable through lengthy reverse engineering work with the objective of understanding the original computer system enough to decode the most original electronic data possible.^[16]

• Category:Lost works
• Lost artworks
• Lost literary work
• Rare groove
• Archival science
• Media archaeology
• Media preservation
• Data archaeology
• Data preservation
• Digital preservation
• Orphan work
• List of unpublished books