It could be argued that much of evolution is really coevolution. Organisms do not exist in an ecological vacuum, but as parts of a network of interacting species. A given species may compete with others for access to prey species used as food, while itself serving as food to predator and parasite species. Natural selection will drive reciprocal evolutionary changes between interacting species. Across its geographical range, a species will encounter different local networks, since the same set of species do not co-occur everywhere. Thus, coevolutionary outcomes will vary in space, forming a geographical mosaic shaped by local adaptation and gene flow. This is the theme of John Thompson's new book, in which the author develops a conceptual framework for the study of coevolution.