The genus Rattus is of central interest to many different fields of biological and medical science but there is significant uncertainty over its evolutionary history and taxonomic content.We explore the content of Rattus using three approaches: 1) a mitochondrial phylogeny based on wider taxon sampling than any previous analysis,including rare and extinct species sequenced from museum specimens; 2) broad genomic sampling for a reduced number of species including potentially close or embedded genera; 3) analysis of dental and cranial shape.We assess the results against three principal criteria for generic delineation – monophyly,lineage age,and adaptive congruency.Our results indicate that Rattus can be defined in a way that satisfies the criteria of monophyly and adaptive congruency,and also retains the major species of biomedical and management concern,namely the Brown Rat (Rattus norvegicus) with its domesticated laboratory strains,the Black or House Rats (Rattus rattus and relatives) ,the Ricefield Rat (R.argentiventer) ,Pacific Rat (R.exulans) and Himalayan Rat (R.nitidus) ,as well as the Australo-Papuan Rattus radiation.However,some species currently placed in Rattus clearly fall outside of this definition and need to be transferred to other genera.