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.

Their scientific name, Callinectes sapidus, means "savory beautiful swimmer." Blue crabs are found in brackish coastal lagoons and estuaries from Nova Scotia, through the Gulf of Mexico, and as far south as Uruguay.