Coatis (from Tupí), also known as coatimundis (/koʊˌɑːtɪˈmʌndi/), are members of the family Procyonidae in the genera Nasua and Nasuella (comprising the subtribe Nasuina). They are diurnal mammals native to South America, Central America, Mexico, and the Southwestern United States. The name "coatimundi" comes from the Tupian languages of Brazil, where it means "lone coati". Locally in Belize, the coati is known as "quash".

Adult coatis measure 33 to 69 cm (13 to 27 in) from head to the base of the tail, which can be as long as their bodies. Coatis are about 30 cm (12 in) tall at the shoulder and weigh between 2 and 8 kg (4.4 and 17.6 lb), about the size of a large house cat. Males can become almost twice as large as females and have large, sharp canine teeth. The measurements above relate to the white-nosed and South America coatis. The two species of mountain coati are smaller.

All coatis share a slender head with an elongated, flexible, slightly upturned nose, small ears, dark feet, and a long non-prehensile tail used for balance and signaling.

Ring-tailed coatis have either a light brown or black coat, with a lighter underpart and a white-ringed tail in most cases. Coatis have a long brown tail with rings on it which are anywhere from starkly defined like a raccoon's to very faint. As in raccoons but not ring-tailed cats and cacomistles, the rings go completely around the tail. Coatis often hold the tail erect; it is used as such to keep troops of coatis together in tall vegetation. The tip of the tail can be moved slightly on its own, as is the case with cats, but it is not prehensile as is that of the kinkajou, another procyonid.

Coatis have bear- and raccoon-like paws and walk plantigrade like raccoons and bears (on the soles of the feet, as do humans). Coatis have nonretractable claws. Coatis also are able to rotate their ankles beyond 180°, in common with raccoons and other procyonids (and others in the order Carnivora and rare cases among other mammals); they are therefore able to descend trees head first. (Other animals living in forests have acquired some or all of these properties through convergent evolution, including members of the mongoose, civet, weasel, cat, and bear families.)

The coati snout is long and somewhat pig-like—part of the reason for its nickname, the "hog-nosed raccoon". It is also extremely flexible and can rotate up to 60° in any direction. They use their noses to push objects and rub parts of their body. The facial markings include white markings around the eyes and on the ears and snout.

Coatis have strong limbs to climb and dig and have a reputation for intelligence, like their fellow procyonid, the raccoon. Unlike the nocturnal raccoons, however, most coatis are diurnal, although some may exhibit cathemeral behavior. They prefer to sleep or rest in elevated places and niches, like the rainforest canopy, in crudely built sleeping nests.

Overall, coatis are widespread, occupying habitats ranging from hot and arid areas to humid Amazonian rainforests or even cold Andean mountain slopes, including grasslands and bushy areas. Their geographical range extends from the southwestern U.S. (southern Arizona, New Mexico, and Texas) through northern Uruguay. Around 10 coatis are thought to have formed a breeding population in Cumbria, UK.