A flounder is a type of flatfish, found in most of the world's oceans. There are a number of varieties of flounder, but all of them share general characteristics which make them quite distinctive. Flounder is eaten by a number of cultures, and considered to be quite delicious. Flounder are among the more bizarre fish species found in shallow water, and tend to fascinate people who stumble across them.

Flounder, like all flatfish, have very flattened bodies. They begin life as small larvae with one eye on each side, but as the larvae mature one of the eyes migrates so that the fish has two eyes on one side. Many species of flounder have their eyes on the left, although some are right sided flounders. After the eye has migrated, the young flounder begins to flatten, and the bottom part of the fish turns pale while the top part grows mottled and sandy colored, green, or sometimes blue. Some flounders are capable of changing coloration slightly for camouflage.

The flounder looks very strange, with both eyes squashed in together at the upper part of the head, a small jaw, and distinct dorsal and lower fins as well as a fanning tail. The body of the fish usually yields two fillets, both of which provide delicate pale meat which is delicious when cooked, although it should only be cooked briefly, and is best when prepared in a pan. Flounder will flake apart if grilled, and this preparation is not recommended.

Flounder eat plankton and other fish species, and will burrow into the ocean bottom to conceal themselves while they wait for prey. Flounder are remarkably good at blending in with backgrounds, and are very successful predator species, as they are fast swimmers. Flounder can be found in a wide range of climates, from warm tropical waters to cold Arctic regions, and are usually found close to shore in fairly shallow water.

After maturing at approximately two years of age, flounder migrate in the early fall to spawn. The larvae drift into estuaries where they mature into adult flounder and become bottom dwellers.

World stocks of flounder appear to be stable, and the fish is not heavily commercially harvested. Many species are not harvested at all, due to size and boniness, while others are sustainably fished and do not appear to be suffering. Flounder have maintained a very broad biological diversity, and enforced quotas on flounder species have assisted with this.