This article summarizes our current knowledge of changes in the intestinal microbiota in elderly people and centenarians.Age-related processes comprise specific changes in the intestinal microbiota and related metabolic alterations. They result in 'inflamm-aging', which is associated with age-related inflammatory processes and diseases, including cachexia, frailty, cancer, and metabolic as well as neurological diseases. Age-related microbial changes consist of an increase in proteolytic bacteria and a decrease in saccharolytic bacteria. These changes are associated with sarcopenia and longevity, and might be attenuated by pre and probiotics. These findings could explain, at least in part, why probiotics have been successfully used in elderly people for the treatment of respiratory and gastrointestinal infections, and for the enhancement of vaccination responses.The intestinal microbiota changes with age. These changes are of relevance in regard to morbidity and mortality in the elderly population. Dietetic (probiotics, prebiotics) and other lifestyle interventions might delay, or even reverse, such alterations.