The common shelduck (Tadorna tadorna) is a waterfowl species of the shelduck genus Tadorna. It is widespread and common in the Palearctic, in Europe and northwest Africa mainly breeding on temperate coasts, saline pools and estuaries, and in Asia on inland salt lakes; increasingly it is also using open freshwater habitats inland. Wintering is in temperate to subtropical regions.

The common shelduck was formally named by the Swedish naturalist Carl Linnaeus in 1758 in the tenth edition of his Systema Naturae under the binomial name Anas tadorna. Linnaeus largely based his description on "The Sheldrake or Burrough-Duck" that had been described and illustrated in 1731 by the English naturalist Eleazar Albin. The specific epithet comes from the French word Tadorne for this species, a name that was used by the French naturalist Pierre Belon in 1555. It may originally derive from Celtic roots meaning "pied waterfowl", essentially the same as the English "shelduck". Linnaeus specified the locality as Europe but restricted this to Sweden in 1761. The common shelduck is now placed in the genus Tadorna that was introduced in 1822 by the German zoologist Friedrich Boie. The species is monotypic, with no subspecies being recognised.

The common shelduck resembles a small short-necked goose in size and shape. It is 55–65 cm long and with a wingspan of 100–120 cm, with a reddish-pink bill, pink feet, a white body with chestnut patches and a black belly, and a dark green head and neck. The wing coverts are white, the primary remiges black, and the secondaries black with a strong green iridescent reflection in good light (only showing in flight). The outer tertial feather is orange-brown, with the inner tertials white. The underwings are white, except for the flight feathers, which are black. The sexes are similar, but the female is slightly smaller, usually with some white flecks on the green face, while the male is particularly crisply coloured in the breeding season, his bill bright red and bearing a prominent knob at the base of the bill.

The ducklings are white, with blackish-brown cap, hindneck and wing and back patches. Juveniles are similarly coloured, greyish above and mostly white below, but already have the adult's wing pattern.

The call is a loud honk.

This is a bird which breeds in the temperate Palearctic region. It has increased and spread markedly since the mid 20th century; at that time in Europe it was strongly restricted to coasts, estuaries and other saline habitats, but is now widespread inland in open freshwater wetlands. It has also spread northwards; in the mid 20th century, it only reached north to 66°N latitude in Norway, but by 2020 had spread along the entire Norwegian coast and into northwestern Russia, including since 2000 in the Murmansk area and the White Sea. Breeding has also expanded south, with extensive colonisation of the Iberian Peninsula, where it formerly only wintered. Much of the increase is thought to be related to improved protection from hunting, but also increased eutrophication of estuaries and wetlands increasing the availability of food. In northwest Africa, breeding is restricted to Tunisia, but it is more widespread in winter west to Morocco.

Asian populations migrate to subtropical areas in winter, south to northern India and southern China, but this species is largely resident in Europe, apart Scandinavian and some eastern European populations which migrate southwest, and from movements to favoured late summer moulting grounds, such as the Wadden Sea on the north German coast.

The common shelduck is common around the coastline of Great Britain and Ireland (where it is known simply as the shelduck), where it frequents salt marshes and estuaries. It frequently nests in rabbit burrows.