Rattus is a genus of muroid rodents, all typically called rats. However, the term rat can also be applied to rodent species outside of this genus.

Species and description: The best-known Rattus species are the black rat (R. rattus) and the brown rat (R. norvegicus). The group is generally known as the Old World rats or true rats and originated in Asia. Rats are bigger than most Old World mice, which are their relatives, but seldom weigh over 500 g in the wild.

Taxonomy of Rattus: The genus Rattus is a member of the giant subfamily Murinae.

The genus Rattus proper contains 64 extant species. A subgeneric breakdown of the species has been proposed, but does not include all species.

Species: Phylogeny: The following phylogeny of selected Rattus species is from .

Evolution: Molecular evidence suggests that Rattus originated in the Late Miocene and that it experienced an exceptionally rapid burst of diversification during the Pleistocene epoch.

Fossil species: In contrast to the large number of living species, as of 2024, just four fossil species have been placed in Rattus proper:

• Rattus baoshanensis - Late Pliocene China
• Rattus jaegeri - Late Pliocene to Early Pleistocene Thailand
• Rattus pristinus - Early Pleistocene China
• Rattus miyakoensis - Late Pleistocene Japan