Microbial ecosystems are the life support system for the planet, and it is important to understand how microbial species will adapt in response to the selective pressures applied by humans and the changing climate. A lot of what we know about the rates and genetic mechanisms of adaptation comes from studies of single-species microbial cultures evolving in the laboratory. However, we know that natural populations of microbes nearly always evolve in the presence of other species, and can evolve by taking up DNA from their environment. In this talk, I will describe evolution experiments with multiple, co-evolving species of fungi, bacteria and bacteriophage, and experiments that incorporate horizontal gene transfer. I present results that show how the context of the microbial community can dramatically alter the outcomes of evolution.