Swimfins, swim fins, fins or flippers are finlike rubber or plastic shoes worn over the foot to assist and expedite movement through the water in water sports activities such as bodyboarding, bodysurfing, kneeboarding, swimming, and various types of diving.

Polymaths such as Leonardo da Vinci and Benjamin Franklin had toyed with the concept, but Louis de Corlieu in France and Owen Churchill in the United States, working independently of each other, were the first to make them a practical reality. Churchill's design caught the attention of the US Navy which wanted to issue it to their underwater demolition teams in the early 1940s; and fins of his design can be found in just about any sporting goods store or surf shop as of 2004.

Different types of fins eventually evolved to address the unique requirements of each community using them. Scuba divers, in particular, need large, wide fins to enable them to overcome the water resistance caused by their diving equipment; snorkelers need lightweight, flexible fins; ocean swimmers, bodysurfers, and lifeguards favor designs that stay on their feet when moving through large surf.

See also: monofin