A gerbil is a small mammal of the order Rodentia. Once known simply as "desert rats", the gerbil subfamily includes about 110 species of African, Indian, and Asian rodents, including sand rats and jirds, all of which are adapted to arid habitats. Most are primarily diurnal (though some, including the common household pet, do exhibit crepuscular behavior), and almost all are omnivorous.

The word "gerbil" is a diminutive form of "jerboa", though the jerboas are an unrelated group of rodents occupying a similar ecological niche.

One Mongolian species, Meriones unguiculatus, also known as the clawed jird, is a gentle and hardy animal that has become a popular pet. It was first brought from China to Paris, France in the 19th century, and became a popular house pet. It was then brought to the United States in 1954 by Dr. Victor Schwentker for use in research.

Gerbils are typically between six and 12 inches (150 and 300 mm) long, including the tail, which makes up about one-half of their total length. One species, the great gerbil, or Rhombomys opimus, originally native to Turkmenistan, can grow to more than 16 inches (400 mm). The average adult gerbil weighs about 2.5 oz. (70 g).