For some decades now, bacteria known as probiotics have been added to various foods because of their beneficial effects for human health. The mechanism of action of probiotics is related to their ability to compete with pathogenic microorganisms for adhesion sites, to antagonize these pathogens or to modulate the host's immune response. The potential application of probiotics includes prevention and treatment of various health conditions and diseases such as gastrointestinal infections, inflammatory bowel disease, lactose intolerance, allergies, urogenital infections, cystic fibrosis, various cancers, reduction of antibiotic side effects, in oral health such as prevention of dental caries, periodontal diseases and oral malodour and many other effects which are under investigation. The results of many of these clinical investigations suggests that probiotics may be useful in preventing and treating various health conditions and diseases. However, many of these clinical studies require validation so as to apply these results to clinical realm. The role of clinical trials is instrumental in such investigations and in near future the results of such trials will decide the usefulness of probiotics in health and disease. This article strives to summarize the currently available data on the potential benefits of probiotics in health and disease.