The snow leopard (Panthera uncia) is a species of large cat in the genus Panthera of the family Felidae. The species is native to the mountain ranges of Central and South Asia. It is listed as Vulnerable on the IUCN Red List because the global population is estimated to number fewer than 10,000 mature individuals and is expected to decline about 10% by 2040. It is mainly threatened by poaching and habitat destruction following infrastructural developments. It inhabits alpine and subalpine zones at elevations of 3,000–4,500 m (9,800–14,800 ft), ranging from eastern Afghanistan, the Himalayas and the Tibetan Plateau to southern Siberia, Mongolia and western China. In the northern part of its range, it also lives at lower elevations.

Taxonomically, the snow leopard was long classified in the monotypic genus Uncia. Since phylogenetic studies revealed the relationships among Panthera species, it has since been considered a member of that genus. Two subspecies were described based on morphological differences, but genetic differences between the two have not yet been confirmed. It is therefore regarded as a monotypic species. The species is widely depicted in Kyrgyz culture.

The Old French word once, which was intended to be used for the Eurasian lynx (Lynx lynx), is where the Latin name uncia and the English word ounce both originate. Once is believed to have originated from a previous form of the word lynx through a process known as false splitting. The word once was originally considered to be pronounced as l'once, where l' stands for the elided form of the word la ('the') in French. Once was then understood to be the name of the animal. The word panther derives from the classical Latin panthēra, itself from the ancient Greek πάνθηρ pánthēr, which was used for spotted cats.

Felis uncia was the scientific name used by Johann Christian Daniel von Schreber in 1777 who described a snow leopard based on an earlier description by Georges-Louis Leclerc, Comte de Buffon, assuming that the cat occurred along the Barbary Coast, in Persia, East India and China. The genus name Uncia was proposed by John Edward Gray in 1854 for Asian cats with a long and thick tail. Felis irbis, proposed by Christian Gottfried Ehrenberg in 1830, was a skin of a female snow leopard collected in the Altai Mountains. He also clarified that several leopard (P. pardus) skins were previously misidentified as snow leopard skins. Felis uncioides proposed by Thomas Horsfield in 1855 was a snow leopard skin from Nepal in the collection of the Museum of the East India Company.

Uncia uncia was used by Reginald Innes Pocock in 1930 when he reviewed skins and skulls of Panthera species from Asia. He also described morphological differences between snow leopard and leopard skins. Panthera baikalensis-romanii proposed by a Russian scientist in 2000 was a dark brown snow leopard skin from the Petrovsk-Zabaykalsky District in southern Transbaikal.

The snow leopard was long classified in the monotypic genus Uncia. They were subordinated to the genus Panthera based on results of phylogenetic studies.

Until spring 2017, there was no evidence available for the recognition of subspecies. Results of a phylogeographic analysis indicate that three subspecies should be recognised:

This view has been both contested and supported by different researchers.