Proteus may refer to:
- In mythology
- Proteus, a Greek god who is the son of Poseidon
- Proteus of Egypt, an Egyptian king in a version of the story of Helen of Troy
- King Proteus, a mythical Greek ruler, featured in the story of Bellerophon
- In science
- Proteus (bacterium), a genus of Proteobacteria responsible for many human urinary tract infections.
- Olm (Proteus anguinus), a genus of small cave-dwelling amphibian
- Proteus, a genus of trilobites
- Proteus syndrome, a very rare congenital disorder known mostly for its most famous sufferer Joseph Merrick (the Elephant Man)
- Proteus (alchemy), the "first matter" (prima materia), usually the metal mercury
- Proteus (moon), a natural satellite of Neptune
- Proteus, a cultivar of Clematis introduced in 1876
- The plant genus Protea, with the form-multiplicity of its species, was named by Linnaeus after the Greek god Proteus, who could change his form at will.
- Proteus (Satellite), a French multimission satellite platform
- Proteus, the oldest Slovenian general purpose scientific journal
- In fiction
- Proteus (character), a comics android who with visual or memory reference, can transform into anything alive or inert
- Proteus (comics), a Marvel Comics mutant
- Proteus (DC comics), a Steve Ditko creation
- Proteus (film), a film by Canadian director John Greyson
- Proteus, the miniaturized submarine that is injected in a human being's bloodstream in the 1966 movie Fantastic Voyage
- Dr. Paul Proteus, the main character in Player Piano by Kurt Vonnegut
- Proteus IV, a villainous supercomputer in the Dean Koontz novel Demon Seed
- Proteus, a character in the play The Two Gentlemen of Verona by William Shakespeare
- Proteus, the Prime Minister in The Apple Cart by George Bernard Shaw
- Vehicles
- USS Proteus (AS-19), a U.S. Navy submarine tender
- Proteus a prototype wave adaptive modular vessel
- A type of diver propulsion vehicle; there are at least two makes called Proteus:
- Scaled Composites Proteus, an experimental aircraft
- Other
- Proteus (mobile marketing company), a mobile company that provides SMS and WAP marketing products
- Proteus (instant messaging client), client software for Mac OS X
- Proteus (design software), software for microprocessor simulation, schematic capture and PCB design developed by Labcenter Electronics
- Proteus (machine), a "sound and light machine" designed by Synthetic Systems
- E-MU Proteus, a popular rackmount ROMpler synthesizer
- Proteans (body language), a class of subtle body language flirting signals
- Proteus (Kadon game), a board game by Kadon
- Proteus (Steve Jackson game), a board game by Steve Jackson Games
- Proteus (Laboratory Information Management System), a computer program for running a laboratory
