In the book, we offer summary and discussion on the advances in understanding of pathophysiological mechanisms of microbial host interactions in human diseases. We will not only discuss intestinal bacterial community, but also viruses, fungi and oral microbiome. Microbiome studies will facilitate diagnosis, functional studies, drug development and personalized medicine. Thus, this book will further highlight the microbiome in the context of health and disease, focusing on mechanistic concepts that underlie the complex relationships between host and microbes.