Sheathbill, the common name of a family of shore birds found on the antarctic shores and subantarctic islands of the Atlantic and Indian oceans. The sheathbills are plump, snow-white birds about 14 to 17 inches (36–43 cm) in length. They have pink-rimmed eyes and short, stubby bills, which are covered at the base with a horny sheath. There are only two species in the family—the white sheathbill, which has a yellow bill, and the lesser sheathbill, which has a black bill and is slightly smaller than the white sheathbill.

Sheathbills feed on seaweeds, mussels, small crustaceans, and the eggs and sickly young of penguins. They build a nest of grass in rock crevices and under boulders. Two or three pale brown eggs with gray or black speckles are laid in the nest. The eggs hatch in about 28 days. The young chicks are covered with a gray down.

Sheathbills make up the family Chionididae. The white sheathbill is Chionia alba; the lesser sheathbill, C. minor.