Arthropod-borne viruses (arboviruses) are important causes of human and animal diseases globally and in Australia. The transmission of these viruses requires alternate replication in mosquito vector and a susceptible mammalian host. Although infection leads to an immune response in both hosts, viruses still manage to replicate to sufficiently high levels. Some of the interactions between virus and host have been identified in mammals; however, the mechanisms employed by viruses for successful transmission in mosquitoes is less understood. Research is currently underway to understand this arms race between mosquito and virus, which determines the mechanism of vector competence for mosquitoes. Identifying and understanding these mechanisms will provide new insight into how viruses are transmitted by mosquitoes.