The guinea pig (Cavia porcellus) is a domesticated form of the cavy and is native to in South America. It is believed to have been domesticated during pre-Incan times from a wild species that lived in Peru. It is not, in fact, a pig but is a rodent, a relative of mice, rats and hamsters.

Like other rodents, guinea pigs' teeth do not have nerves and grow continuously, like fingernails. Wild guinea pigs (Cavia tschudii) are found in the Andes and Peru where they live in burrows and graze on vegetation.

There are several theories about why they are called Guinea Pigs: When first imported to England they were meant to be sold for a guinea a piece and they were known as pigs due to their squealing noises. Another theory is that the word guinea is actually a corruption of Guyana, a country in South America where domestic breeds of Cavia are kept and are referred to as pigs. A third theory proposes that the name may refer to Guineamen, who were in the slave trade and may have been the first to import the animals from South America to England.

There are many types of domestic guinea pigs, most breeds are recognizable by their hair type. English and American breeds have smooth short hair, Angoras have smooth long hair, and Peruvians have rough long hair. Varieties of breeds are typically distinguished by hair colors and markings. Domestic guinea pigs are still an important source of meat for some people in the Andes. Cavies are also used in a multitude of research roles including biochemical, physiological and pharmacological. In western culture, guinea pigs are regarded as docile, loveable pets. They can't be taught to roll over and fetch, but they'll lie in someone's lap for hours. A full-grown guinea pig is about 6-10 inches long, weighs, 2-4 pounds, and lives about 4-8 years.