- Doomsday is a Christian term for the end of the world.
- The Domesday Book is 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 is an alien comic book supervillain best known for having killed Superman.
- Doomsday is the term for the day of the week defined in the Doomsday algorithm.
- The Doomsday argument is a statistical argument suggesting that humanity will be extinct sooner rather than later.
- Reference to a Doomsday event.
- The Doomsday Engine is 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.