Females tend to have more markings than males, which may become nearly completely white as they age. Young snowy owls are generally darker and more heavily marked than adults. Snowy owls have yellow eyes and their legs and feet are covered in white feathers that protect them from the cold weather. Snowy owls are the largest bird species in the arctic, 63 to 73 cm long with an average wingspan of 170 cm

The female begins laying eggs at 2-day intervals. Clutch size is normally 3 to 11 white eggs, but can be as large as 16 when prey are extremely abundant. The female incubates the eggsuntil the chicks hatch after 32 to 34 days of incubation. The eggs hatch approximately every other day leading to a wide range in size and age of chicks within a nest. Chicks begin to leave the nest before they can fly, 14 to 26 days after hatching. The parents continue to feed them for 5 to 7 weeks until they are able to hunt for themselves.

Snowy owl fossils have been found as far south as the Tropic of Cancer, and are believed to have originated in that region.