Cooperation among individuals of the same population directed against competing populations (cooperative warfare) is widespread in animals and plants. What happens in the microbial world is much less understood. Microbes can interact with one another through chemical signals, but little is known about the nature of their interactions, particularly outside the laboratory. On page 1228 of this issue, Cordero et al. (1) present a detailed analysis of ecological interaction networks, population structures, and genetic relatedness of microbes in the wild. They suggest that cooperative warfare is common in the microbial world.