The domestication of small mammals to keep as pets is a relatively recent development, arising only after large-scale industrialization. Historically, Western society was more agrarian than today, with rodents as a whole seen as vermin that were carriers for disease and a threat to crops. Animals that hunted such pests, such as terriers, ferrets and cats, were prized.

Many small animals kept as household pets are rodents, including: fancy mice, fancy rats, hamsters (golden hamsters and dwarf hamsters), gerbils (Mongolian jirds and duprasi gerbils), common degus, common chinchillas, and guinea pigs (cavies). Non-rodents, including rabbits, hedgehogs and sugar gliders, are also kept.

Some of these small mammals are prohibited from being kept as pets in certain jurisdictions for being invasive; California, Hawaii, Alberta and New Zealand have strict regulations to protect their native environments and agricultural operations. Gerbils, degus, and domesticated rats have various prohibitions on their ownership.

The definition of a "small mammal" differs, but is generally accepted as all mammals weighing less than 5 kilograms (11 lb).

The term "pocket pet" is used for a small, pocket-sized mammal (sometimes also categorized as a "small and furry" in the pet industry) commonly kept as a household pet.

Guinea pigs (cavy) have perhaps been kept the longest as pets among rodents. While historically they were domesticated as a food staple for the native Inca people, they were imported to Europe as early as the mid-16th century, shortly after Spain conquered Peru. As an oddity from the New World, they were afforded a special status, and seen as house pets, rather than vermin or food. While their popularity was initially limited to the wealthy, their prodigious reproductive habits ensured that they spread throughout the middle classes shortly after their introduction; guinea pig burial places (not scattered bones—as would be found with an eaten animal) have been found in archaeological digs in early modern middle-class suburbs.

Guinea pigs do not store their food. They typically travel in groups, or herds, scavenging for grass and other vegetation. Guinea pigs should not consume meat, as they rely on a fiber diet of plants. They are commonly active during dawn or dusk when they are less likely to encounter predators (crepuscular). As pack animals in the wild, the domestic Guinea pig also thrives when kept with one or more companions (except boars in the presence of a sow). They live off a diet consisting of grass hay and food pellets, typically synthesized from timothy hay. Like humans, Guinea pigs cannot synthesize their own vitamin C, making their food intake their only source of vitamin C. A lack of vitamin C will often cause fatal scurvy. At merely four weeks old, female Guinea pigs become fertile and may produce as many as four to five litters a year. With an average gestation period of 59–72 days, a female Guinea pig may become pregnant again in as few as 6 hours after giving birth. However, there are a lot of concerns related to Guinea pig pregnancy. Guinea pigs live to be around 4 to 5 years old.

Fancy mice were popular pets in Japan during the 18th century, due in large part to the abundance of color mutations in wild mice. In 1787, a book on this hobby, The Breeding of Curious Varieties of the Mouse, was published by Chobei Zenya, a Kyoto money exchanger. Over time, the tradition spread from Japan to Europe, and in 1895 the National Mouse Club was established in England.