Peccaries (also known as javelinas, by the Portuguese name javali and Spanish jabalí or pecarí) are medium-sized mammals of the family Tayassuidae. Peccaries are members of the artiodactyl suborder Suina, as are swine (Suidae) and possibly hippopotami. They are found in the southwestern area of North America and throughout Central and South America. Peccaries usually measure between 90 and 130 cm in length (3 to 4 feet), and a full-grown adult usually weighs between about 20 and 40 kilograms (44 to 88 pounds).

People often confuse peccaries, which are found in the Americas, with pigs which originated in Afro-Eurasia, especially since some domestic pigs brought by European settlers have escaped over the years and now run wild as razorback hogs in many parts of the United States.

Peccaries are medium-sized animals, with a strong superficial resemblance to pigs. Like pigs, they have a snout ending in a cartilagenous disc, and eyes that are small relative to their head. Also like pigs, they use only the middle two digits for walking, although, unlike pigs, the other toes may be altogether absent. Their stomach is non-ruminating, although it has three chambers, and is more complex than that of pigs.

Peccaries are omnivores, and will eat small animals, although their preferred food consists of roots, grass, seeds, and fruit. One of the ways to tell apart pigs and peccaries is the shape of the canine tooth, or tusk. In European pigs the tusk is long and curves around on itself, whereas in peccaries, the tusk is short and straight. The jaws and tusks of peccaries are adapted for crushing hard seeds and slicing into plant roots, and they also use their tusks for defense.

By rubbing the tusks together they can make a chattering noise that warns potential predators not to get too close. Peccaries, indeed, are aggressive enough in temperament that, unlike Eurasian pigs, they cannot be domesticated as they are likely to injure humans. Indeed in recent years in North-western Bolivia near Madidi National Park there have been reports of people being seriously injured and killed by large groups of peccaries.

Peccaries are social animals, and often form herds. Over 100 individuals have been recorded for a single herd of white-lipped peccaries, but collared and Chacoan peccaries usually form smaller groups. Such social behavior seems to have been the situation in extinct peccaries as well.

Peccaries have scent glands below each eye and another on their back, though these are believed to be rudimentary in Pecari maximus. They use the scent to mark herd territories, which range from 75 to 700 acres (2.8 km2). They also mark other herd members with these scent glands by rubbing one against another. The pungent odor allows peccaries to recognize other members of the herd, despite their myopic vision.

Today there are four living species of peccary, found from the southwestern United States through Central America and into South America and Trinidad.

The Collared Peccary (Pecari tajacu) occurs from the southwestern United States into South America and the island of Trinidad. They are found in all kinds of habitats, from dry arid scrublands to humid tropical rainforests. They are sometimes called the "musk hog" because of their strong odor. In some areas of the southwestern United States they have become habituated to human beings and live in relative harmony with them in such areas as the suburbs of cities where there are still areas of brush and undergrowth to move through. They are generally found in squadrons of eight to 15 animals of various ages. They will defend themselves if they feel threatened but otherwise tend to ignore human beings. They defend themselves with their long tusks, which sharpen themselves whenever the mouth opens or closes.

Throughout the states of Arizona, New Mexico, and Texas, collared peccaries are known as javelinas. They are often seen around people's houses, with herds of them sometimes seen walking across driveways or porches. In some neighborhoods, they even live in backyards.

A second species is the White-lipped peccary (Tayassu pecari), which is found in the rainforests of Central and South America.

The third species, the Chacoan peccary (Catagonus wagneri), is the closest living relative to the extinct Platygonus pearcei. It is found in the dry shrub habitat or Chaco of Paraguay, Bolivia, Argentina and Southern Brazil. The Chacoan peccary has the unusual distinction of having been first described based on fossils and was originally thought to be only an extinct species. In 1975 the animal was discovered to still be alive and well in the Chaco region of Paraguay. The species was well known to the native people.

A fourth species, the Giant Peccary (Pecari maximus) was recently discovered in the Brazillian Amazon by Dutch biologist Marc van Roosmalen. Though recently discovered by science it has been known to the local Tupi people as Caitetu Munde, which means "great peccary which lives in pairs." It is thought to be the largest extant peccary, and can grow to 1.2 meters in length. Its fur is completely dark gray, with no collars whatsoever. Unlike other peccaries it lives in pairs, or with one or two offspring.

Peccaries first appeared in the fossil records of the Late Eocene or Early Oligocene periods in Europe. Fossils have later been found in all continents except Australia and Antarctica. It became extinct in the Old World sometime after the Miocene period.

Although they are common in South America today, peccaries did not reach that continent until about three million years ago during the Great American Interchange, when the Isthmus of Panama formed, connecting North America and South America. At that time, many North American animals — including peccaries, llamas and tapirs — entered South America, while some South American species, such as the ground sloths, migrated north.