The illustrated mosquito primary keys are intended to help those who are themselves entomologists to identify their specimens, at least to the correct species group. The secondary keys, among the descriptions, may prove a little more difficult, but, if used with the summary of diagnostic characters in the short diagnosis at the beginning of the description of each species, they should enable most members of species groups to be correctly identified. These secondary keys, unlike the primary ones, include species that occur in surrounding countries and are related to those known in Malaysia, so that in most cases all members of a species group are included in a key. Only brief notes are given on these species in surrounding countries, full descriptions are limited to those occurring in Malaysia.