any of about 45 species of Old World tropical birds constituting the family Bucerotidae (order Coraciiformes). They are noted for the presence, in a few species, of a bony casque, or helmet, surmounting the prominent bill. Hornbills range in size from 40 cm (16 inches), in the smaller Tockus species, to 160 cm (63 inches), in the great hornbill (Buceros bicornus). They are typically large-headed, with thin necks, broad wings, and long tails. The plumage is brown or black, usually with bold white markings.

Hornbills nest in cavities, usually in large trees. In all species except the two ground hornbills (Bucorvus), the male walls the female in the nest, closing the hole with mud, except for a small opening through which he passes food. After the eggs hatch, the female breaks out, but the young may be walled in again.