Callinectes sapidus (from the Ancient Greek κάλλος,"beautiful" + nectes, "swimmer", and Latin sapidus, "savory"), the blue crab, Atlantic blue crab, or regionally as the Maryland blue crab, is a species of crab native to the waters of the western Atlantic Ocean and the Gulf of Mexico, and introduced internationally.

Callinectes sapidus, also known as the Blue Crab, is a commercially important species through much of its native range. Its range extends from Cape Cod to northern Argentina, including Bermuda and the West Indies. Adults are occasionally caught as far north as the Gulf of Maine and Nova Scotia, Canada.

Call­inectes sapidus, the blue crab, is a bot­tom-dweller found in a va­ri­ety of habi­tats rang­ing from the salti­est water of the gulf to al­most fresh water of the back bays. Es­pe­cially com­mon in es­tu­ar­ies, this species ranges into fresh water, and may be found off­shore.

Callinectes Sapidus, a crustacean of the decapods order that also includes lobsters, crayfish, shrimps and prawns, was first observed in the Mediterranean Sea in 1949, where it was probably transported by the ballast waters of transoceanic ships.