Storks are large, long-legged, long-necked wading birds with long, stout bills. They belong to the family called Ciconiidae. They are the only family in the order Ciconiiformes, which was once much larger and held a number of families including herons and ibises.
Storks are large to very large waterbirds. They range in size from the marabou, which stands 152 cm (60 in) tall and can weigh 8.9 kg (20 lb) the Abdim's stork, which is only 75 cm (30 in) high and only weighs 1.3 kg (2.9 lb). Their shape is superficially similar to the herons, with long legs and necks, but they are heavier-set. There is some sexual dimorphism (differences between males and females) in size, with males being up to 15% bigger than females in some species (for example the saddle-billed stork), but almost no difference in appearance. The only difference is in the colour of the iris of the two species in the genus Ephippiorhynchus.