An important concept to emerge recently, or at least become widely recognized, relates to the role of genetics in the vector competence of mosquitoes for arboviruses. It is now quite evident that females within a single mosquito species can vary significantly in their peroral susceptibility and/or their ability to transmit an arbovirus that is normally vectored by that mosquito species. Research done since 1928 has provided a broad base of knowledge on the susceptibility and resistance of numerous mosquito species and strains to various arboviruses. The biological transmission of arboviruses by fully competent vector mosquitoes requires that the virus initiate infection in the mesenteron following the ingestion of an infective blood meal, escape from the mesenteron and disseminate via the hemolymph throughout the hemocele, establish infection in the salivary glands with or without secondary amplification in extra mesenteronal tissues, and be released into the salivary gland secretions where it can be transmitted to a vertebrate host during the feeding process.