Mosquitoes, ticks, and fleas are common blood-feeding pests. Many species of mosquitoes, ticks, and fleas are also vectors—living organisms that can transmit pathogens between humans or between animals and humans. In humans, vector-borne diseases associated with mosquitoes, ticks, and fleas can range from mild infections to serious, even life-threatening illnesses. Preventive measures to stop the spread of these diseases are an important public health priority in the United States and globally. Many effective prevention efforts are relatively simple, such as pet care, home and yard maintenance, choosing the correct clothing, and appropriate use of insect repellents and insecticides. Additionally, large-scale initiatives to address issues such as the effects of climate change and inadequate sanitation are needed.