The book brings a completely different perspective than available books by combining the information gained from the human genome with that derived from parallel metagenomic studies, and new results from investigating the effects of these microbes on the host immune system. Although there are a number of books that focus on the human genome that are currently available, there are no books that bring to the forefront the mix of the human genome and the genomes and metagenomes of the microbial species that live within and on us.