The condition and function of gastrointestinal (GI) tract are essential to our well being. Probiotics are defined as the microbial food supplements, which beneficially affect the host by improving its intestinal microbial balance. Probiotics are the functional food ingredients. They are used therapeutically to improve lactose tolerance and to prevent diarrhoea (especially viral diarrhoea in infants, antibiotic-associated diarrhoea, Clostridium difficile-associated diarrhoea and traveler's diarrhoea). Clinical studies suggest that probiotics might be useful in stimulation of the immune system, prevention of allergic diseases, control of GI tract inflammatory diseases and cancer prevention. Probiotic microbial species act by changing the composition of the gut microbionta. The use of non-digestible oligosaccharides (prebiotics) can fortify intestinal microflora and stimulate their growth. This review encompasses information regarding probiotic strains, prebiotics and commercially products (functional food), which can be useful in improving our health.