The Asian Koel (Linnaeus) is a member of the cuckoo order of birds, the Cuculiformes.

It is a mainly resident breeder in tropical Southern Asia from India, Bangladesh and Sri Lanka to South China . The Asian Koel is a bird of light woodland and cultivation.

The Asian Koel is omnivorous, consuming a variety of insects, caterpillars, eggs and small vertebrates. Adults feed mainly on fruit.

The Asian Koel is a large, long-tailed, cuckoo measuring 39-46 cm (15-18 in). The male of the nominate race is glossy bluish-black, with a pale greenish grey bill, the iris is crimson, and it has grey legs and feet. The female of the nominate race is brownish on the crown and has rufous streaks on the head. The back, rump and wing coverts are dark brown with white and buff spots.

The Asian Koel is a brood parasite that lays its eggs in the nests of crows and other hosts, who raise its young. The breeding season of Koel is March to August in South Asia.

The Koel is not known to lay eggs in an empty host nest and a study found that the first Koel eggs were laid, on average, within one and half days of the laying of the host's first egg. The chicks of the Koel hatched about 3 days ahead of the host chicks. Koels usually lay only an egg or two in a single nest but as many as seven to eleven eggs have been reported from some host nests. A female may remove a host egg before laying. Eggs hatch in 12 to 14 days. The young Koel does not always push out eggs or evict the host chicks, and initially calls like a crow. The young fledge in 20 to 28 days.

They will sometimes defend fruiting trees that they forage in and chase away other frugivores. It has been chosen as the state bird by the southern Indian state of Puducherry .They is very vocal during the breeding season with a range of different calls. The familiar song of the male is a repeated koo-Ooo. The female makes a shrill kik-kik-kik... call. The bird is a widely used symbol in Indian poetry.