The ring ouzel (Turdus torquatus) is a mainly European member of the thrush family Turdidae. It is a medium-sized thrush, 23–24 centimetres (9.1–9.4 in) in length and weighing 90–138 grams (3.2–4.9 oz). The male is predominantly black with a conspicuous white crescent across its breast. Females are browner and duller than males, and young birds may lack the pale chest markings altogether. In all but the northernmost part of its range, this is a high-altitude species, with three subspecies breeding in mountains from Ireland east to Iran. It breeds in open mountain areas with some trees or shrubs, the latter often including juniper and other treeline conifers, rowan, bilberry, heather, and hairy alpenrose. It is a migratory bird, leaving the breeding areas to winter in southern Europe, North Africa and Turkey, typically in mountains with junipers. The typical clutch is 3–6 brown-flecked pale blue or greenish-blue eggs. They are incubated almost entirely by the female, with hatching normally occurring after 13 days. The altricial, downy chicks fledge in another 14 days and are dependent on their parents for about 12 days after fledging.

The ring ouzel is omnivorous, eating invertebrates, particularly insects and earthworms, some small vertebrates, and a wide range of fruit. Most animal prey is caught on the ground. During spring migration and the breeding season, invertebrates dominate the adult's diet and are also fed to the chicks. Later in the year, fruit becomes more important, particularly the common juniper.

With an extensive range and a large population, the ring ouzel is evaluated as least concern by the International Union for Conservation of Nature (IUCN). There are signs of decline in several countries; suspected causes including climate change, human disturbance, hunting and outdoor leisure activities. Loss of junipers may also be a factor in some areas. Natural hazards include predation by mammalian carnivores and birds of prey, and locally there may also be competition from other large thrushes such as the common blackbird, mistle thrush and fieldfare.

"Ouzel" is an old name for the common blackbird, the word being cognate with the German Amsel. "Ouzel" may also be applied to a group of superficially similar but more distantly related birds, the dippers, the European representative of which is sometimes known as the water ouzel. "Ring Ouzel" was first used by John Ray in his 1674 Collection of English Words not Generally Used and became established with his 1678 book The Ornithology of Francis Willughby of Middleton in the County of Warwick. As with the English term, the scientific name also refers to the male's prominent white neck crescent, being derived from the Latin words turdus, "thrush", and torquatus, "collared". Old and local names for the ring ouzel include "fell blackbird", "hill blackbird", "moor blackbird", "rock ouzel" and "mountain blackbird".

The ring ouzel was first described by Carl Linnaeus under its current scientific name in his 1758 10th edition of Systema Naturae. He noted earlier descriptions by Francis Willughby and Eleazar Albin, both of whom gave it the name Merula torquata.

There are 104 species of medium to large thrushes in the genus Turdus. They are characterised by rounded heads, medium or longish pointed wings, and usually melodious songs.

A 2020 study of the genetics of Turdus suggested that the genus arose about 9.37 million years ago (Mya), expanding out of Africa around 7.2 Mya, and diverging into Palearctic and Oriental groups about 5.7 Mya. Further radiation from Africa to the Americas followed at about 5.3 Mya. Details of the study suggest that the ring ouzel, a member of the Eurasian group, may be more closely related to Naumann's and dusky thrushes than to the superficially more similar common blackbird.

The ring ouzel has three recognised subspecies: