Ecologists bemoan the dearth of theory in ecology, in particular, the lack of an overarching, general theory. These complaints largely are unjustified. The components of a general theory of ecology have existed for the past half century; ecologists simply have failed to explicitly recognize them. We present a general theory of ecology and show how it relates to ecology’s numerous constituent theories and models. The general theory consists of a description of the domain of ecology and a set of fundamental principles. The domain of ecology is the spatial and temporal patterns of the distribution and abundance of organisms, including causes and consequences. Fundamental principles are broad statements about the patterns that exist and the processes that operate within a domain. The seven fundamental principles of the theory of ecology are: the heterogeneous distribution of organisms, interactions of organisms, contingency, environmental heterogeneity, finite and heterogeneous resources, the mortality of organisms, and the evolutionary cause of ecological properties. These principles are the necessary and sufficient elements for a general theory of ecology. The propositions of any constituent theory of ecology can be shown to be a consequence of these fundamental principles along with principles from other science domains. The general theory establishes relationships among constituent theories through shared fundamental principles. The next challenge is to develop and integrate unified, constituent theories and to establish the relationships among them within the framework established by the general theory.