Rats are various medium-sized, long-tailed rodents of the superfamily Muroidea. "True rats" are members of the genus Rattus, the most important of which to humans are the black rat, Rattus rattus, and the brown rat, Rattus norvegicus. Many members of other rodent genera and families are also called rats and share many characteristics with true rats.

Specially bred rats have been kept as pets at least since the late 19th century. Pet rats are typically variants of the species Brown rat, but Black rats and Giant pouched rats are also known to be kept. Pet rats behave differently than their wild counterparts depending on how many generations they have been kept as pets. Pet rats do not pose any more of a health risk than pets such as cats and dogs. Tamed rats are generally friendly and can be taught to perform selected behaviors.