Doomsday can refer to:

• Doomsday, a Christian term for the end of the world.
• The Domesday Book, a census of England taken in the 11th century. The BBC Domesday Project was an attempt to create an equivalent of the Domesday book for the late 20th century.
• Doomsday, an alien comic book supervillain best known for having killed Superman.
• Doomsday, the term for the day of the week defined in the Doomsday algorithm.
• The Doomsday argument, a statistical argument suggesting that humanity will be extinct sooner rather than later.
• a Doomsday event.
• The Doomsday Engine, an open source game engine, a source port of the original Doom engine. Ports of the computer games Doom, Heretic and HeXen using the Doomsday Engine are called jDoom, jHeretic and jHexen, respectively.
• Doomsday is also a 1927 novel by Warwick Deeping.
• Doom's Day is a national holiday in the fictional country of Latveria, celebrated whenever its ruler Victor von Doom feels like it.
• The callsign of Etienne Montclair, a pilot in the Wing Commander universe. Of Maori descent, Montclair earned his callsign for his dour and pessimistic attitude.