The text is completely rewritten, based on the author's Medical and Veterinary Entomology (edition 2, 1923). In the interval of sixteen years much new material has become available in medical entomology. This is true especially in the fields related to public health, notably with reference to two of the greatest plagues of mankind, malaria and bubonic plague, both with insect vectors, the ubiquitous mosquito and the pestiferous flea, respectively. The book makes extensive use of the results of experiments and of the relation to public health of various insects. Nearly 100 pages deal with mosquitoes alone, discussing their classification, life history, food, flight, longevity, biting habits, mating and oviposition, and the special characteristics of the more banal species. Keys to the genera of culicids and to the species of anophelines of the United States are provided. A chapter is devoted to mosquitoes as vectors of disease. In addition to the