Bucerotiformes, consisting of hornbills, has a total of 54 bird species world over, divided into two families (Bucerotidae, Bucorvidae) and nine genera. Hornbills are strictly 'old world' birds, meaning their range extends from Africa across India and Asia to Papua New Guinea. Hornbills are characterized by large bills, often topped with casques and a two-lobed kidney. Bucerotiformes species (Hornbills) are the only birds in which the first two vertebrae (the axis and atlas) are fused together. Males are about 18% larger than females.

Hornbills generally breed as monogamous pairs. They nest in existing holes or crevices, either in trees or rocks. The female seals herself up inside the cavity and then proceeds to molt all her flight feathers in one go while she is incubating the eggs. In some cases the males help seal the female in. Part of the entrance will be sealed up with mud before the female gets into the nest. When the entrance is only just big enough for her to get through, she gets into the cavity and remains there. The hole is then further sealed up from inside using food items and feces. The end result is a narrow slit opening which is just big enough for the male to offer food. The female and the young are then fed by the male who brings food to the nest and passes it inside. The two Bucorvidae species nest in open cavities - rolling stumps, etc - the nest is not sealed and the female emerges daily to preen and defecate. The larger Bucerotiformes bird species can be very long-lived.

India has ten species of Hornbills, all belonging to the family Bucerotidae:

Family: Bucerotidae

Narcondam Hornbill Aceros narcondami - local resident
Rufous-necked Hornbill Aceros nipalensis - local resident
Plain-pouched Hornbill Aceros subruficollis - local resident (Nicobar)
Wreathed Hornbill Aceros undulatus - widespread resident
Brown Hornbill Anorrhinus tickelli - local resident
Oriental Pied-Hornbill Anthracoceros albirostris - widespread resident
Malabar Pied-Hornbill Anthracoceros coronatus - widespread resident
Great Hornbill Buceros bicornis - widespread resident
Indian Grey-Hornbill Ocyceros birostris - widespread resident
Malabar Grey-Hornbill Ocyceros griseus - widespread resident