Hantavirus (Bunyaviridae family) are present worldwide and are the causative agent of haemorrhagic fever with renal or pulmonary syndrome. These viruses are transmitted by rodents with asymptomatic infection which thus act as an excellent reservoir. Molecular epidemiology indicates that Hantavirus may have evolved in three ways: mutations within the genome, reassortment of the segmented genome between two closely related Hantavirus, and genomic recombination, a relatively rare phenomenon among negative stranded RNA viruses. Each virus is carried primarily by a specific rodent host. This observation is confirmed by phylogenetic analyses: the evolution tree of the different Hantavirus, based on viral genomic sequences has been shown to mirror the evolution tree of their specific rodents, based on sequences of mitochondrial DNA. Altogether these data suggest that an ancestral Hantavirus infected a specific rodent, early during evolution, and was subsequently submitted to the same evolutionary pressure as the rodent host.