This book includes studies aimed at determining design interventions in which the composition of microbiota may be modulated to achieve a specific microbial profile beneficial to overall host behavior. In addition, this compilation summarises and critically discusses recent literature on the evaluation of changes in the microbiota associated with liver diseases, aiming to evaluate which alterations could be involved in the initiation and progression of liver disease. The authors emphasize the importance of promoting a balanced microbiome to maintain or improve oral health effectively. In order to fully understand the progression of oral diseases, it is essential to evaluate the microbiome together with genetic, immunological and environmental factors.