Microorganisms came into existence over 3.8 billion years ago and they are found everywhere today. The roles of these organisms in the environment, their ecology, have been finely honed by evolutionary processes over the complete span of life on earth. Most evolutionary and ecological theory has been developed with macroorganisms as the model organisms. Considering that evolution has been acting on microorganisms longer than all other organisms combined it is the thesis of this book that insights into both evolution and ecology can be obtained through the study of microorganisms. Here we examine the evolutionary ecology of microorganisms from individual, population, and community perspectives. Species interactions including competition, predation, parasitism, and mutualisms as well as microbial communication through quorum sensing are examined through the lens of evolutionary ecology. Microbial sex and reproduction, nutrient cycling, and cheating are considered through the same lens. Optimal foraging, genome reduction, novel evolutionary mechanisms, bacterial speciation, r and K selection and many other topics are measured from a microbial perspective. The result is a context for understanding microbes in nature and a framework for microbiologists working in industry, medicine, and the environment.