This book presents the latest methods, gives broad and systematic coverage of most mucosal systems and diseases, and takes a fresh perspective that looks at the functional aspects of change in the microbiome. The study of microbiome and microbial metabolites and their roles in host mucosal immunology is a rapidly developing area of research. One major way in which the microbiome influences the host is through altered metabolism. Metabolites, readily available to the host, engender significant consequences. Microbial metabolites have been shown to impact the disease processes in both proximal and distal organs, including the brain in several neurocognitive disorders.