The white-throated kingfisher (Halcyon smyrnensis) also known as the white-breasted kingfisher is a tree kingfisher, widely distributed in Asia from the Sinai east through the Indian subcontinent to China and Indonesia. This kingfisher is a resident over much of its range, although some populations may make short distance movements. It can often be found well away from water where it feeds on a wide range of prey that includes small reptiles, amphibians, crabs, small rodents and even birds. During the breeding season they call loudly in the mornings from prominent perches including the tops of buildings in urban areas or on wires.

The white-throated kingfisher is one of the many birds that were first formally described by the Swedish naturalist Carl Linnaeus in 1758 in the tenth edition of his Systema Naturae. He coined the binomial name Alcedo smyrnensis. Linnaeus cited Eleazar Albin's Natural History of Birds published in 1738 that included a description and a plate of the "Smirna Kingfisher". Albin's specimen was preserved in alcohol and had been collected by the botanist William Sherard who served as the British Consul at Smyrna between 1703 and 1716. The present genus Halcyon was introduced by the English naturalist and artist William Swainson in 1821. Halcyon is a name for a bird in Greek mythology generally associated with the kingfisher. The specific epithet smyrnensis is an adjective for the city of Smyrna (now İzmir in Turkey).

Five subspecies are recognised:

The brown-breasted kingfisher (H. gularis) of the Philippines is usually now considered as a separate species. Support for this treatment was provided by a molecular study published in 2017 that found that H. s. gularis was more closely related to the Javan kingfisher (H. cyanoventris) than it was to the white-throated kingfisher. They were split as distinct species by the IUCN Red List and BirdLife International in 2014, and the International Ornithological Congress followed suit in 2022. The races H. s. perpulchra and H. s. fokiensis are sometimes included in H. s. fusca.

Local names include Baluchistan: aspi chidok; Sindhi: dalel; Hindi: kilkila, kourilla; Himachal Pradesh: neela machhrala; Punjabi: wadda machhera; Bengali: sandabuk machhranga; Assamese: māsorokā, মাছৰোকা; Cachar: dao natu gophu; Gujarati: kalkaliyo, safedchati kalkaliyo; Marathi: khundya; Tamil: vichuli; Telugu: lakmuka, buchegadu; Malayalam: ponman; Kannada: Minchulli(ಮಿಂಚುಳ್ಳಿ),rajamatsi; Sinhalese: pilihuduwa.

This is a large kingfisher, 27–28 cm (10.6–11.0 in) in length. The adult has a bright blue back, wings and tail. Its head, shoulders, flanks and lower belly are chestnut, and the throat and breast are white. The large bill and legs are bright red. The flight of the white-throated kingfisher is rapid and direct, the short rounded wings whirring. In flight, large white patches are visible on the blue and black wings. Sexes are similar, but juveniles are a duller version of the adult.

This species forms a superspecies with Halcyon cyanoventris and most major works recognize four geographic races. They vary clinally in size, the shades of blue on the mantle which is more greenish in smyrnensis and fusca and more blue or purplish in saturatior. H. s. gularis of the Philippines has only the neck and throat white. It is sometimes treated as a distinct species, H. gularis. Race fusca is found in Peninsular India and Sri Lanka and is slightly smaller, bluer and with a darker brown underside than the nominate race found in northwestern India. Race saturatior is found in the Andaman Islands and is larger with darker brown underparts. Race perpulchra (not always recognized) is found in northeastern India and is smaller than fusca with paler underparts. Albinism has been noted on occasion.

The white-throated kingfisher is a common species in a variety of habitats, mostly open country in the plains (but has been seen at 7500 ft in the Himalayas) with trees, wires or other perches. The range of the species is expanding.