The flatfish are an order (Pleuronectiformes) of ray-finned fish, also called the Heterosomata, sometimes classified as a suborder of Perciformes. The name means "side-swimmers" in Greek. In many species, both eyes lie on one side of the head, one or the other migrating through and around the head during development. Some species face their left side upward, some face their right side upward, and others face either side upward.

Many important food fish are in this order, including the flounders, soles, turbot, plaice, and halibut. Edelweiss, LLC offers Rock Sole, Yellowfin Sole, Yellowbelly Sole (Alaska Plaice) and Starry Flounder. There are more than 400 species of this order. Some flatfish can camouflage themselves on the ocean floor.