The black stork (Ciconia nigra) is a large bird in the stork family Ciconiidae. It was first described by Carl Linnaeus in the 10th edition of his Systema Naturae. Measuring on average 95 to 100 cm (37 to 39 in) from beak tip to end of tail with a 145-to-155 cm (57-to-61 in) wingspan, the adult black stork has mainly black plumage, with white underparts, long red legs and a long pointed red beak. A widespread but uncommon species, it breeds in scattered locations across Europe (predominantly in Portugal and Spain, and central and eastern parts), and east across the Palearctic to the Pacific Ocean. It is a long-distance migrant, with European populations wintering in tropical Sub-Saharan Africa, and Asian populations in the Indian subcontinent. When migrating between Europe and Africa, it avoids crossing broad expanses of the Mediterranean Sea and detours via the Levant in the east, the Strait of Sicily in the center, or the Strait of Gibraltar in the west. An isolated non-migratory population lives in Southern Africa.

Unlike the closely related white stork, the black stork is a shy and wary species. It is seen singly or in pairs, usually in marshy areas, rivers or inland waters. It feeds on amphibians, small fish and insects, generally wading slowly in shallow water stalking its prey. Breeding pairs usually build nests in large forest trees—most commonly deciduous but also coniferous—which can be seen from long distances, as well as on large boulders, or under overhanging ledges in mountainous areas. The female lays two to five greyish-white eggs, which become soiled over time in the nest. Incubation takes 32 to 38 days, with both sexes sharing duties, and fledging takes 60 to 71 days.

The black stork is considered to be a species of least concern by the International Union for Conservation of Nature, but its actual status is uncertain. Despite its large range, it is nowhere abundant, and it appears to be declining in parts of its range, such as in India, China and parts of Western Europe, though increasing in others such as the Iberian Peninsula. Various conservation measures have been taken for the black stork, like the Conservation Action Plan for African black storks by Wetlands International. It is also protected under the African-Eurasian Waterbird Agreement and the Convention on International Trade in Endangered Species of Wild Fauna and Flora. On 31 May 1968, South Korea designated the species as natural monument 200.

English naturalist Francis Willughby wrote about the black stork in the 17th century, having seen one in Frankfurt. He named it Ciconia nigra, from the Latin words for "stork" and "black" respectively. It was one of the many species originally described by Swedish zoologist Carl Linnaeus in the landmark 1758 10th edition of his Systema Naturae, where it was given the binomial name of Ardea nigra. It was moved to the new genus Ciconia by French zoologist Mathurin Jacques Brisson two years later. The word stork is derived from the Old English word storc, thought to be related to the Old High German storah, meaning "stork", and the Old English stearc, meaning "stiff".

The black stork is a member of the genus Ciconia, or typical storks, a group of seven extant species, characterised by straight bills and mainly black and white plumage. The black stork was long thought to be most closely related to the white stork (C. ciconia). However, genetic analysis via DNA–DNA hybridization and mitochondrial cytochrome b DNA by Beth Slikas in 1997 found that it was basal (an early offshoot) in the genus Ciconia. Fossil remains have been recovered from Miocene beds on Rusinga and Maboko Islands in Kenya, which are indistinguishable from the white and black storks.

The black stork is a large bird, measuring between 95 and 100 cm (37 and 39 in) in length with a 145-to-155 cm (57-to-61 in) wingspan, and weighing around 3 kg (6.6 lb). Standing as tall as 102 cm (40 in), it has long red legs, a long neck and a long, straight, pointed red beak. It bears some resemblance to Abdim's stork (C. abdimii), which can be distinguished by its much smaller build, predominantly green bill, legs and feet, and white rump and lower back. The plumage is black with a purplish green sheen, except for the white lower breast, belly, armpits, axillaries and undertail coverts. The breast feathers are long and shaggy, forming a ruff which is used in some courtship displays. The black stork has brown irises, and bare red skin around its eyes. The sexes are identical in appearance, except that males are larger than females on average. Moulting takes place in spring, with the iridescent sheen brighter in new plumage. It walks slowly and steadily on the ground and like all storks, it flies with its neck outstretched.

The juvenile resembles the adult in plumage, but the areas corresponding to the adult black feathers are browner and less glossy. The scapulars, wing and upper tail coverts have pale tips. The legs, bill and bare skin around the eyes are greyish green. It could possibly be confused with the juvenile yellow-billed stork, but the latter has paler wings and mantle, a longer bill and white under the wings.

During the summer, the black stork is found from Eastern Asia (Siberia and northern China) west to Central Europe, reaching Estonia in the north, Poland, Lower Saxony and Bavaria in Germany, the Czech Republic, Hungary, Italy and Greece in the south, with an outlying population in the central-southwest region of the Iberian Peninsula (Extremadura and surrounding provinces of Spain, plus Portugal). It is migratory, wintering in tropical Africa and Asia, although certain populations of black storks are sedentary or dispersive. An isolated population exists in Southern Africa, where the species is more numerous in the east, in eastern South Africa and Mozambique, and is also found in Zimbabwe, Eswatini, Botswana and less commonly Namibia.