In spite of the extensive attention given by research workers to aphids no comprehensive review has been published covering all aspects of aphid biology. A few small books exist on certain aspects of nomenclature, ecology, physiology and natural enemies. Aphid biology is studied by many specialists, all representing their own area of interest, therefore the only way to present this comprehensive review is by the multi-author approach. This three-volume work is compiled in a similar way to the first books in the series World Crop Pests: Spider Mites. The volumes contain contributions by more than 40 authors. In this first volume an account is given on morphology and systematics, anatomy, genetics, life cycles, ways of life, reproduction and polymorphism and interaction with the environment. These topics are followed by an in-depth study of evolution of aphids, especially in connection with the evolution of plants. In addition processes governing the development of population structure and speciation are elicited.