Gut microbiota are responsible for a variety of metabolic activities including food digestion and production of biologically active substances. Moreover, several recent works, including our own, have also shown that gut microbiota play an important role not only in the development of brain function but also in the pathology of stress-related diseases and neurodevelopmental disorders. In this review, we focus on the interaction between gut microbes and the brain-gut axis and introduce some basic concepts and recent developments in this area of research.