An observer is one who engages in observation or in watching an experiment.

Observer may also refer to:

• Observer (novel), a 2023 science fiction novel by Robert Lanza and Nancy Kress
• Observer (video game), a cyberpunk horror video game
• Observer (Mystery Science Theater 3000), a fictional television character
• Observers, beings in the television show Fringe

• "Observer", a song by Gary Numan on his album The Pleasure Principle
• "The Observer", a track from The Flaming Lips' 1999 album The Soft Bulletin
• The Observers, an alternative name for reggae session band Soul Syndicate

• The Observer, a UK Sunday newspaper & magazine
• The Observer (disambiguation), multiple publications including newspapers, magazines & fiction
• The APS Observer, a member magazine of the Association for Psychological Science (APS)

• Observer (general relativity)
• Observer (quantum physics)
• Observer (special relativity)
• Observer (meteorological)
• Observer pattern, a design pattern used in computer programming
• State observer in control theory, a system that models a real system in order to provide an estimate of its internal state

• The Observer type in the Enneagram of Personality model
• Donald Alaster Macdonald (1859–1932), Australian journalist who wrote under the pseudonym 'Observer'

• Observer effect (disambiguation)
• National Observer (disambiguation), a variety of publications
• The Observer (disambiguation)
• United Nations Military Observer
• All pages with titles containing Observer