Our microflora is an individual personal feature, providing a distinct tag to individuals. However, our intestinal microbiome is strongly affected by genetic, nutritional, and other external factors, and evolves with age. An effect of different microbial patterns on health appears very likely as there seem to be specific changes of intestinal microflora associated with various diseases. Specific microbial tags may thus be used as biomarkers of disease: to diagnose it, to monitor its evolution, and eventually to predict its response to treatment. This scenario opens the opportunity for targeting intestinal microflora using probiotics, both for prevention and treatment of an increasing number of conditions. Probiotic therapy is applied either as an adjunct to other treatments or as primary therapy, and evidence of efficacy is accumulating in several conditions, affecting either the intestine or nonintestinal organs. This publication provides an update on probiotics directed at physicians, biologists, biotechnologists, and researchers working in the food industry and agriculture, as well as in the environmental and basic sciences.