A flipper is a digitless, typically flat limb evolved for movement through water. Various creatures have evolved flippers, for example most fish (although for fish the usual term is fin), as well as certain mammals (whales, pinnipeds) and reptiles (turtles).

Flippers sometimes occur in non-flippered species as the result of a birth defect. For example, the morning-sickness drug thalidomide caused some infants to be born with flipper-like limbs.