The Collared Kingfisher is a medium-sized kingfisher belonging to the subfamily Halcyoninae, the tree kingfishers. It varies from blue to green above while the underparts can be white or buff. There is a white collar around the neck, giving the birds its name. Some races have a white or buff stripe over the eye while others have a white spot between the eye and bill. There may be a black stripe through the eye. The large bill is black with a pale yellow base to the lower mandible.
Females tend to be greener than the males. Immature birds are duller than the adults with dark scaly markings on the neck and breast.
It is most commonly found in coastal areas, particularly in mangrove swamps. It also inhabits farmland, open woodland, grassland and gardens. In some parts of its range, especially on islands, it can be seen further inland, ranging into forest or into mountain areas. Birds often perch conspicuously on wires, rocks or bare branches.
Small crabs are the favoured food in coastal regions but a wide variety of other animals are eaten including insects, worms, snails, shrimps, frogs, lizards, small fish and sometimes other small birds as well.