Mosquitoes are flies in the insect family Culicidae which are the primary arthropod vectors of human diseases worldwide. They are particularly known as vectors of the agents of malaria, yellow fever, dengue, and filariasis in tropical countries. This chapter explores the biology, ecology, and disease relationships of mosquitoes, including discussion of the various mosquito groups (genera) and where each breeds, what animal hosts they feed on, and the like. Lastly, each of the major mosquito-borne diseases is presented and discussed, including their geographic distributions, mosquito vectors, and comments about their treatment, prevention, and control.