The gut-brain axis is a well-known entity that is important in maintaining homeostasis. In the last decade, we have seen the importance of the microbiota as one of the critical regulators of brain function, and this has led to the appreciation of the importance of a distinct microbiota- gut-brain axis. This axis is under research for various biological and physiological bases of psychiatric, neurodevelopmental, age-related, and neurodegenerative disorders. The microbiota and the brain communicate via various routes, including the vagus nerve, immune system, tryptophan metabolism, and the entero-endocrinal system through the production of various microbial metabolites. Many factors can influence microbiota
composition in early life, including infection in utero, mode of delivery, use of antibiotic medications, the nature of nutritional provision, environmental stressors, and genetic composition. Various research is ongoing regarding the role of microbiota in many conditions, including autism, anxiety, obesity, schizophrenia, Parkinson’s disease, and Alzheimer’s disease. In this article, we attempt to briefly elucidate the gut microbiota, its composition, its importance in the gut-brain axis, its
associated pathways, and the diseases caused by microbiota dysbiosis. 

Keywords: Gut microbiota; gut-brain axis; ENS; psychobiotics; faecal microbiota transplantation