The barn owl (Tyto alba) is the most widely distributed species of owl in the world and one of the most widespread of all species of birds, being found almost everywhere in the world except for the polar and desert regions, Asia north of the Himalayas, most of Indonesia, and some Pacific Islands. It is also known as the common barn owl, to distinguish it from the other species in its family, Tytonidae, which forms one of the two main lineages of living owls, the other being the typical owls (Strigidae).
Phylogenetic evidence shows that there are at least three major lineages of barn owl: one in Europe, western Asia, and Africa; one in southeastern Asia and Australasia; and one in the Americas; as well as some highly divergent taxa on various islands. Accordingly, some authorities divide barn owls into the western barn owl, for the group in Europe, western Asia, and Africa; the eastern barn owl for the group in southeastern Asia and Australasia; and the American barn owl for the group in the Americas.
Some taxonomic authorities classify barn owls differently, recognising up to five separate species; and further research needs to be done to resolve the disparate taxonomies. There is considerable variation of size and colour among the approximately 28 subspecies, but most are between 33 and 39 cm (13 and 15 in) in length, with wingspans ranging from 80 to 95 cm (31 to 37 in). The plumage on the head and back is a mottled shade of grey or brown; that on the underparts varies from white to brown and is sometimes speckled with dark markings. The face is characteristically heart-shaped and is white in most subspecies. This owl does not hoot, but utters an eerie, drawn-out screech.