This edited volume studies gut microbiota peculiarities in elderly, in senescence-related and environmental-related alterations of gut microbiota in chronic diseases. Aging, as a physiological process mediated through several regulatory pathways and transcription factors, is generally speaking associated to a relentless functional decline and increasing risk of chronic diseases. Growing data on gut microbiota quali-quantitative changes in aging gut, and the opportunity to study by advanced NGS and metabolomic technologies, now offers novel horizons to link such changes to disease risks and to theoretically the weapons for gut microbiota intervention as an effective therapeutic tool. Chapters are divided into clear sections, starting with the aging perspective, then moving from chronic diseases to neurodegenerative diseases and cancer. The final parts focusses on interventions.