Portunidae is a family of crabs which contains the swimming crabs. Its members include well-known shoreline crabs such as the blue crab (Callinectes sapidus) and velvet crab (Necora puber).

Portunid crabs are characterised by the flattening of the fifth pair of legs into broad paddles, which are used for swimming. This ability, together with their strong, sharp claws, allows many species to be fast and aggressive predators.

Swimming crabs reach their greatest species diversity in the Pacific and Indian Oceans.^{[citation needed]} Portunidae consists of the following subfamilies and genera: