Brain related disorders are among the most challenging health issues of our time. The development of effective therapeutic and preventive strategies for these disorders relies on a comprehensive understanding of the underlying causative mechanisms. And, until recently, these mechanisms have remained somewhat elusive. The newly discovered pivotal role of the intestinal microbiome in brain health, functionality, and resistance to disease is revolutionizing neuroscience. The Microbiome and the Brain, through the contributions of some of the most forward thinking researchers and clinicians in the field, comprehensively reveals the leading edge of our understanding of the fundamental role of gut microbes and their metabolites in a wide array of seemingly diverse brain issues including Alzheimer’s disease, autism, multiple sclerosis, and mood disorders. In addition, mechanisms defining these relationships are explored along with a presentation of the state-of-the-art as it relates to interpretation of relevant laboratory assessments. Finally, novel therapeutic opportunities, derived from this exciting science are presented.