A proposed project to sequence the microorganisms that inhabit our bodies could have a huge impact on human health. Much as we might like to ignore them, microbes have colonized almost every inch of our bodies, living in our mouths, skin, lungs, and gut. Indeed, the human body has 10 times as many microbial cells as human cells. They’re a vital part of our health, breaking down otherwise indigestible foods, making essential vitamins, and even shaping our immune system. Recent research suggests that microbes play a role in diseases, such as ulcers, heart disease, and obesity.