The incidence and prevalence of vector-borne diseases have risen dramatically in most developing countries in all regions of the world. In the past decade, malaria has shown the greatest resurgence. Other resurging diseases include schistosomiasis, African trypanosomiasis, filariasis, onchocerciasis, dengue, plague, mosquito-borne encephalitis, relapsing fever and leishmaniasis. Insecticides continue to provide the major weapon against most vector diseases, but the problem of vector resistance, placed on their use have severely handicapped many vector control programs. In meeting the vector control needs of member nations of the WHO, the WHO Division of Vector Biology and Control provides advisory services, technical assistance, training and conducts and supports vector research and development on an international scale. Integrated vector control approaches involving water management, biological control, genetic control, and other non-pesticidal methods are receiving increasing priority, but the urgent need for effective insecticides is expected to continue for an indefinite period.