Gut microbiota are an area recently targeted by modern biomedical research. In fact, during the last five years, there has been increasing evidence related to the role of gut microbiota as remarkable symbiotic partners critical for the maintenance of good health. Several factors cause alterations in gut microbiota which are, indeed, accompanied by alterations in the quality of health. Accordingly, gut microbiota dysbiosis has been related to increased susceptibilities to intestinal, cardiovascular, and nervous pathologies. In this manual, you will find the latest studies carried out in the field of microbiota. Overall, the contributions published in this Special Issue further strengthen the essential function of gut microbiota in health and in various diseases.