Pleuronectidae is a family of fishes of the order Pleuronectiformes. The body is compressed from the sides. Eyes in representatives of the family are located on the right side of the head, these are so-called right-sided flounders. However, some species have left-sided (reversed) forms. The pelvic fins are symmetrical, with a narrow base. Eggs do not contain fat droplets, floating, develop in the upper layers or in the water column. In five species, the eggs are benthic. Swim bladder is absent. About 100 species. Inhabit tropical, subtropical, temperate and Arctic waters of the world's oceans. Marine, sedentary bottom and benthic fish. They feed on bottom invertebrates (sea, polar, yellowfin, river flounder), large species (black and white-skinned halibut) are predators. Benthic species are 30-60 cm long, predators up to 5 m and mass up to 300 kg (white-skinned halibut). Pleuronectidae are of great commercial importance. The most valuable of them are halibut.