The utilization of live microorganisms as therapeutics has been gaining increasing attention over the last years with the addition of scientific knowledge on their traditional uses. Probiotics are defined as "live micro-organisms which when administered in adequate amounts, confer a health benefit on the host". The normal intestinal microbiota prevents the colonization of pathogenic bacteria and has important immune functions. It has been hypothesized that the sudden change in the intestinal microbiota that parallels the modern life practices of humans might have contributed to the rise in the incidence of particular diseases. Bacteria and yeasts may be used as probiotics either in the form of a single strain or combination of microorganisms or mixed with prebiotics. Probiotics have been used for various disease states from gastrointestinal diseases to infections and even to diabetes and atopic diseases. Drawing firm conclusions about the clinical efficacy of probiotics is hard because of the heterogeneity of patient populations, probiotic strains, dosages, and commercial preparations. However, probiotics represent a very exciting and promising area of research due to the ever-increasing antibiotic resistance rates and the ability of some probiotics to modify the course of diseases.