The jaguarundi (Herpailurus yagouaroundi; /ˌdʒæɡwəˈrʌndi/ or /ˌʒæɡwəˈrʌndi/) is a wild cat native to the Americas. Its range extends from central Argentina in the south to northern Mexico, through Central and South America east of the Andes. The jaguarundi is a medium-sized cat of slender build. Its coloration is uniform with two color morphs, gray and red. It has an elongated body, with relatively short legs, a small, narrow head, small, round ears, a short snout, and a long tail, resembling mustelids in these respects. It is about twice as large as a domestic cat (Felis catus), reaching nearly 360 mm (14 in) at the shoulder, and weighs 3.5–7 kg (7.7–15.4 lb).

Secretive and alert, the jaguarundi is typically solitary or forms pairs in the wild; however, captive individuals are more gregarious. Unlike other sympatric cats such as the ocelot, the jaguarundi is more active during the day and hunts mainly during daytime and evening hours. Individuals live in large home ranges, and are sparsely distributed within a region. The jaguarundi is an efficient climber, but typically prefers hunting on ground. It feeds on various kinds of prey, especially ground-feeding birds, reptiles, rodents and small mammals. Mating occurs throughout the year, with peaks at different times of the year across the range. After a gestation period of 70 to 75 days, a litter of one to four kittens is born. Lifespans of up to 15 years have been recorded in captivity.

The jaguarundi inhabits a broad array of both closed and open habitats ranging from tropical rainforests and deciduous forests to deserts and thorn scrubs. It is fairly common in Brazil, Peru, and Venezuela, but may be extirpated from the United States. It is listed as least concern on the IUCN Red List, but populations are in decline in many parts of its range due to loss and fragmentation of habitat, as well as persecution for killing poultry.

The common name "jaguarundi" comes from the Old Guarani word yaguarundi, similar to the Old Tupi word yawaum'di, meaning "dark jaguar". The name is pronounced /ˌʒæɡwəˈrʌndi/ or /ˌdʒæɡwəˈrʌndi/. In some Spanish-speaking countries, the jaguarundi is also called gato colorado, gato moro, león breñero, leoncillo and tigrillo. It is also called eyra, gato-mourisco, gato-preto, gato-vermelho and maracajá-preto in Brazilian Portuguese.

In 1803 Étienne Geoffroy Saint-Hilaire described two jaguarundi skins and skulls from unknown locations in Central America and proposed the scientific name Felis yagouarundi. In the 19th and 20th centuries, several more zoological specimens were described:

The generic name Herpailurus was proposed by Nikolai Severtzov in 1858 for the jaguarundi. Later authors classified the jaguarundi in the genus Puma along with the cougar (P. concolor). Phylogeographical analysis of jaguarundi samples from across its range found no genetic evidence for subspecies. In 2017, the IUCN Cat Specialist Group revised felid taxonomy and recognises the jaguarundi as a monotypic taxon of the genus Herpailurus.

The jaguarundi is most closely related to the cougar; the jaguarundi-cougar clade is sister to the cheetah. These three species comprise the Puma lineage, one of the eight lineages of Felidae; the Puma lineage diverged from the rest 6.7 million years ago. The sister group of the Puma lineage is a clade of smaller Old World cats that includes the genera Felis, Otocolobus and Prionailurus.

The three species of the Puma lineage may have had a common ancestor during the Miocene, about 8.25 million years ago. Acinonyx possibly diverged from the lineage in the Americas; some authors alternatively suggest that the cheetah diverged in the Old World.