Your body is more than just you - it is an ecosystem for trillions of tiny microbes. These bacteria, viruses, and other single-celled organisms form communities inside and on your body. Together, these communities make up your microbiome. Your microbiome works with your body to keep your digestive system, immune system, and even your brain working properly. Your microbiome is so important to your survival, you could think of it as an extra organ.