Microbes can produce many of the metabolic resources they need to survive. But because they have permeable cell walls, those resources can leak out into the surrounding environment. Since microbes often live in communities with many other types of microbes, they can also take in the metabolic resources that other microbes have leaked. And, they can respond to their environments, shifting what and how much of some good they produce themselves. In a way, this exchange of goods is its own kind of economy—but it’s one we humans don’t understand well.