A fish is any member of a paraphyletic group of organisms that consist of all gill-bearing aquatic craniate animals that lack limbs with digits. Included in this definition are the living hagfish, lampreys, and cartilaginous and bony fish, as well as various extinct related groups. Most fish are ectothermic ("cold-blooded"), allowing their body temperatures to vary as ambient temperatures change, though some of the large active swimmers like white shark and tuna can hold a higher core temperature. Fish are abundant in most bodies of water. They can be found in nearly all aquatic environments, from high mountain streams (e.g., char and gudgeon) to the abyssal and even hadal depths of the deepest oceans (e.g., gulpers and anglerfish). At 32,000 species, fish exhibit greater species diversity than any other group of vertebrates.

The FISH! philosophy is a workplace management system created by John Christensen. The system was first published as a film, with a spin-off series of books. The central concepts of the system were inspired by the observed work culture at Seattle's Pike Place Fish Market, anecdotes about which are often used as illustrations in the film and books.

Fish are vertebrates with gills that live in water. Related concepts include:

• Fish (food), an important source of protein for humans throughout recorded history
• Fishing, the activity of trying to catch fish

Fish may also refer to:

• Albert Fish (1870–1936), American serial killer and cannibal
• Bert Fish (1875–1943), American judge and ambassador
• Eric Fish (born 1969), singer in Subway To Sally and solo artist
• Fred Fish (1952–2007), American computer programmer
• Fish (Kent cricketer), refers to a noted professional cricketer in the 18th century who was chiefly associated with Kent in the 1760s and 1770s
• Ginger Fish (born 1965), drummer for the band Marilyn Manson
• Hamilton Fish (disambiguation), any of several American politicians
• Henry Smith Fish (1838–1897), New Zealand politician from Dunedin
• Leslie Fish, singer and anarchist
• Mardy Fish (born 1981), American professional tennis player
• Matt Fish (born 1969), American basketball player
• Michael Fish (born 1944), BBC weather presenter
• Michael Fish (fashion designer), UK fashion designer
• Morris Fish (born 1938), Justice of the Supreme Court of Canada
• Nicky Fish (born 1984), Welsh footballer
• Oliver Fish, fictional character on the ABC daytime drama One Life to Live
• Preserved Fish (1766–1846), New York shipping merchant
• Simon Fish (died 1531), 16th century Protestant reformer
• Stanley Fish (born 1938), literary theorist
• Stuyvesant Fish (1851–1923), president of Illinois Central Railroad

Fish! is a text adventure game by Magnetic Scrolls released in .