Dr. Quigley has created a must-have reference on the gut microbiome for the practicing gastroenterologist. A leader in the field of human physiology and digestive disorders, he has laid out the basics on this increasingly important topic, devoting articles to the organization and biology of the human gut microbiome as well as its diagnostic potential. Top international authors have presented articles that discuss the intersection of the gut microbiome and diet and the gut-brain axis. Clinical implications of the gut microbiome are discussed with disease states like IBD, GI cancer, and liver diseases. Finally, the issue ends with the cutting-edge clinical innovation of fecal microbial transplantation. This issue bridges the gap between science and clinical practice and should be an important reference to practicing gastroenterologists.