As humans, we tend to think simplistically about microbes, anthropomorphizing them as either "bad guys," - the germs that cause disease, or as "good guys," the single-celled organisms benefitting us and our world through their metabolic processes. The reality of microbes' relationship with humans is, in Facebook parlance, "complicated," fully embodying the spectrum from friend to foe. Indeed, the same microbe can be fickle about its virulence within a single human host, choosing to enhance the host's life in one moment then threatening to endanger its life in the next. In this talk, we'll explore how a better understanding of the dynamics between microbes and their human hosts offers lessons for us from the very basics of evolutionary biology to applications for medicine and human health.