The Human Microbiome Project and other microbiome projects worldwide have laid an important foundation for understanding the trillions of microbes that inhabits each of our bodies-and how they affect human health. We know that things like diet affect the microbiome, or that obesity is linked to the microbes that live in your gut. Research suggests that microbes may even be associated with autism! However, we need more samples to fully understand how our microbes are linked to health and disease. American Gut gives you the opportunity to participate in the discovery of new scientific knowledge about the microbiome by comparing the microbes in your gut (or in your mouth or on your skin) to those of thousands of participants in the US and elsewhere around the world. American Gut is a project built on open-source, open-access principles. Our data are for the good of scientific understanding and will be shared both with participants and with other scientists.