Functional foods have gained gradual recognition as we learned that healthy diets result from not only eating nutritious foods but from the identification of the mechanisms by which foods modulate metabolism and gut health. Now research is focusing on the area of probiotics. We can say this is the 'golden period' of probiotics as probiotics is not a new word, it was first conceptualized by the Russian Nobel prize winner and father of modern immunology Elie Metchnikoff at the beginning of the 20th century. He believed that the fermenting bacteria in milk products consumed by Bulgarian peasants were responsible for their longevity and good health. Recent research is now catching up with his instincts. Lilly and Stillwell first used the actual word in 1965 as a contrast to the word 'antibiotics.' By the 1970s probiotics were being used in the sense that we know today. As antimicrobial resistance increases into a major public health problem, Antimicrobial peptides are the starting point of multiple efforts to develop new agents that are effective against a variety of microbes but not against mammalian cells. What do probiotics do to the gut? Probiotics protect the mucosal barrier from undesired bacterial colonization through more than one mechanism, which we can classify into three categories: 1) Effects on the bacterial populations and their metabolism. 2) Effects on the intestinal epithelia and their differentiation 3) Effects on the immune cells and their activation. Barrier effects of the microbiota could include competition with a pathogen for a specific receptor. A non-specific steric hindrance caused by the bacteria adhering to the gut wall. The common phenomenon behind this is production of antibacterial substances or competition for metabolic substrates. Probiotics could improve mucosal health by activating the host?s defense mechanisms without stimulating an inflammatory reaction in the intestinal mucous Conclusion: The new age of functional foods and the introduction of the probiotic concept into the food industry have brought new and unforeseen challenges to the design and application of such living solutions to new generation of stable but functional foods. In making probiotic products, for example, relatively long storage in chilled dairy products may seriously hamper the survival of these strains. That means essential organisms targeted to populate the human gut one of the most important issues in health benefit provision by probiotic bacteria. Shell life - the presence of an adequate number of live bacteria at the end of the shell life even more important because this is the essence of the health promoting values. The final stage of development, in which additional bacterial action and their health benefits are being discovered and incorporated into new strains, is just beginning but it is already very clear that the future for this field is promising.