Editors' Summary: Eric Smith in this chapter expands on some of the ideas presented in the previous chapter to outline the field of evolutionary ecology, a rapidly developing area in ecology. Much of the theory is drawn from the animal ecology literature, but the work takes on an added dimension with its application to human populations. Smith points out that both evolutionary ecology and sociobiology are based on natural selection theory, and he recognizes individual benefit as a major criterion for adaptation. However sociobiology is based on genetic theory, while evolutionary ecology focuses on regularities in flexible phenotypic responses to problems and opportunities presented by the environment. Smith argues on logical and empirical grounds that ecological models and environmental variables are more useful in predicting patterns of human adaptation than are the narrowly genetic models of sociobiology. This fits well with Dyson-Hudson's conclusion on theoretical grounds that many human behaviors are based on very open rather than closed genetic programs.