Hamsters are rodents belonging to the subfamily Cricetinae. The subfamily contains about 25 species, classified in six or seven genera.

Hamsters are crepuscular and remain underground during the day to avoid being caught by predators. In the wild, they feed primarily on seeds, fruits, and vegetation, and will occasionally eat burrowing insects. They have elongated cheek pouches extending to their shoulders in which they carry food back to their burrows. Hamsters tend to sleep during the day and are wide awake at night, which may be irritating to some people because of their cage-biting and wheel-running.

Hamster behavior varies depending on their environment, genetics, and interaction with people. Because they are easy to breed in captivity, hamsters are often used as laboratory animals. Hamsters have also become established as popular small house pets, and are sometimes accepted even in areas where other rodents are disliked, and their typically solitary nature can reduce the risk of excessive litters developing in households.