It is necessary to have a healthy gastrointestinal system for human beings and animals to be able to maintain a healthy life. This is realised by the intestinal microflora. Probiotics, prebiotics and synbiotics are used to strengthen useful microflora of intestine. Probiotic microorganisms provide inhibition of pathogenic microorganisms in the body, increase digestibility of feed, enhance the immune system, decrease blood cholesterol level, decrease or limit absorptionof toxic substances and increase the absorption of prebiotics. For having favourable effects of probiotics, it is necessary that probiotic microorganisms maintain the adequate number of viable cells during the shelf life of the product as well as during the gastrointestinal (GI)Ftract transit after consumption. Prebiotics are indigestible carbohydrates that enhance the number and activity of the colon bacteria and the effects of probiotics. Prebiotics used selectively by beneficial microflora in colon prevent potential pathogen microorganisms from multiplying. Probiotics and prebiotics may be used in combination in food products, thereby being called synbiotic. The length of life of probiotic bacteria extends thanks to this combination and they are colonised better in colon. In this compilation, the importance of the effects of prebiotics, probiotics and synbiotics on health of human beings and animals is pointed out