Book excerpt: The Human Biome is a complex and essential biological system within the human body. The adult human harbors some 100 trillion bacteria in his gut alone. Balance of this system is essential to good health. This issue of Clinics in Laboratory Medicine focuses on treatments to realign this balance as well as advances in understanding the system in general. Topics include: Changes in microbiome in GERD; The relationship of microbiome, inflammation, and colon cancer; Gut microbiome and host genetics in Crohn's disease; Association of oral microbiome with head and neck cancer; The vaginal microbiome-disease, genetics and the environment;, The human virome in children and its relationship to febrile illness; Gut microbiome in irritable bowel syndrome; The neonatal microbiome and necrotizing enterocolitis; Fecal microbiota transplantation for clostridium difficile Infection.