Kingfishers are a group of small to medium sized brightly coloured birds in the order Coraciiformes. They have a cosmopolitan distribution, with most species being found in the Old World and Australia. The group is treated either as a single family, Alcedinidae, or as a suborder Alcedines containing three families, Alcedinidae (river kingfishers), Halcyonidae (tree kingfishers), and Cerylidae (water kingfishers). There are roughly 90 species of kingfisher. All have large heads, long, sharp, pointed bills, short legs, and stubby tails. Most species have bright plumage with little differences between the sexes. Most species are tropical in distribution, and a slight majority are found only in forests. They consume a wide range of prey as well as fish, usually caught by swooping down from a perch. Like other members of their order they nest in cavities, usually tunnels dug into the natural or artificial banks in the ground. A few species, principally insular forms, are threatened with extinction.

The kingfishers have a cosmopolitan distribution, occurring throughout the worlds tropics and temperate regions. They are absent from the polar regions and some of the world's driest deserts. A number of species have reached islands groups, particularly those in the south and east Pacific Ocean. The Old World tropics and Australasia are the core area for this group. Europe and North America north of Mexico are very poorly represented with only one common kingfisher (Common Kingfisher and Belted Kingfisher respectively), and a couple of uncommon or very local species each: (Ringed Kingfisher and Green Kingfisher in the southwest USA, Pied Kingfisher and White-throated Kingfisher in SE Europe). The six species occurring in the Americas are four closely related green kingfishers in the genus Chloroceryle and two large crested kingfishers in the genus Megaceryle. Even tropical South America has only five species plus wintering Belted Kingfisher. In comparison, the tiny African country of  The Gambia has eight resident species in its 120 by 20 mi. (192 by 32 km) area.

Individual species may have massive ranges, like the Common Kingfisher, which ranges from Ireland across Europe, North Africa and Asia as far as the Solomon Islands in Australasia, or the Pied Kingfisher, which has a widespread distribution across Africa and Asia. Other species have much narrower ranges, particularly insular species which are endemic to a single small island. The Kofiau Paradise Kingfisher is restricted to the tiny island of Kofiau off New Guinea.

Kingfishers occupy a wide range of habitats. While they are often associated with rivers and lakes, over half the worlds species are found in forests and forested streams. They also occupy a wide range of other habitats. The Red-backed Kingfisher of Australia lives in the driest deserts, although kingfishers are absent from other dry deserts like the Sahara. Other species live high in mountains, or in open woodland, and a number of species live on tropical coral atolls. Numerous species have adapted to human modified habitats, particularly those adapted to woodlands, and may be found in cultivated and agricultural areas, as well as parks and gardens in towns and cities.

The kingfishers feed on a wide variety of items. They are most famous for hunting and eating fish, and some species do specialise in catching fish, but other species take crustaceans, frogs and other amphibians, annelid worms, molluscs, insects, spiders, centipedes, reptiles (including snakes) and even birds and mammals. Individual species may specialise in a few items or take a wide variety of prey, and for species with large global distributions different populations may have different diets. Woodland and forest kingfishers take mainly insects, particularly grasshoppers, whereas the water kingfishers are more specialised in taking fish. The Red-backed Kingfisher has been observed hammering into the mud nests of Fairy Martins to feed on their nestlings. Kingfishers usually hunt from an exposed perch, when a prey item is observed the kingfisher swoops down to snatch it, then returns to the perch. Kingfishers of all three families beat larger prey on a perch in order to kill the prey and to dislodge or break protective spines and bones. Having beaten the prey it is manipulated and then swallowed.

Kingfishers are territorial, some species defending their territories vigorously. They are generally monogamous, although cooperative breeding has been observed in some species. In a few species cooperative breeding is quite common, for example the laughing Kookaburra, where helpers aid the dominant breeding pair in raising the young.

Like all Coraciiformes, the kingfishers are cavity nesters, with most species nesting in holes dug in the ground. These holes are usually in earth banks on the sides of rivers, lakes or man-made ditches. Some species may nest in holes in trees, the earth clinging to the roots of an uprooted tree, or arboreal nests of termites (termitarium). These termite nests are common in forest species. The nests take the form of a small chamber at the end of a tunnel. Nest-digging duties are shared between the sexes. During the initial excavations the bird may fly at the chosen site with considerable force, and birds have injured themselves fatally while doing this. The length of the tunnels varies by species and location, nests in termitariums are necessarily much shorter than those dug into the earth, and nests in harder substrates are shorter than those in soft soil or sand. The longest tunnels recorded are those of the Giant Kingfisher, which have been found to be 8.5 m long.

The eggs of kinfishers are invariably white and glossy. The typical clutch size varies by species; some of the very large and very small species lay as few as two eggs per clutch, whereas others may lay 10 eggs, the average is around three to six eggs. Both sexes incubate the eggs.