The Greylag Goose (also spelled Graylag in the United States), Anser anser, is a bird with a wide range in the Old World. It is the type species of the genus Anser. It was in pre-Linnean times known as the Wild Goose ("Anser ferus"). This species is the ancestor of domesticated geese in Europe and North America. Flocks of feral birds derived from domesticated birds are widespread.
This species is found throughout the Old World, apparently breeding where suitable localities are to be found in many European countries, although it no longer breeds in southwestern Europe. Eastwards it extends across Asia to China. In North America there are both feral domestic geese, which are similar to greylags, and occasional vagrants.
In Great Britain their numbers have declined as a breeding bird, retreating north to breed wild only in the Outer Hebrides and the northern mainland of Scotland. However during the 20th century, feral populations have been established elsewhere, and they have now re-colonised much of England. The breeding habitat is a variety of wetlands including marshes, lakes, and damp heather moors.