The common goldeneye, also simply named goldeneye, is a medium-sized duck of the genus Bucephala. Adult birds have a wingspan of about 80 cm and weigh approximately 1 kg. Females are usually smaller and lighter than males.
The species is named for its golden-yellow eyes. Adult males have a dark head and a circular white patch below the eye, a dark back and a white neck and belly. Adult females have a brown head and a mostly gray body. Both sexes have a distinctive puffy head shape and orange-yellow legs and feet.
Surprisingly, the eyes of the common goldeneye are gray-brown at hatching. They turn purple-blue, then blue, then green-blue as they age. By five months of age, they have become golden-yellow.