This work examines the ecology of aphids, some of which are serious pests of agricultural crops and forest trees. It also considers the relationships of aphids with their host plants, natural environments and the physical environment in relation to certain of the features that aphids developed early in their evolutionary history. In particular, the book explains how the modes of feeding and reproduction of aphids have led to a close and specific association with their host plants and affected the size of individuals and their population structure. Influences on life history patterns, dispersal, population dynamics, species diversity and world-wide distribution are also considered. The book should be of interest to specialists and postgraduates in entomology, ecology, animal reproduction, animal behaviour, pest biology and population biology.