Probiotic microorganisms may affect human health, partly by modulating the immune response. They are commensals, part of the natural human microbiota, or provided within fermented foods or within food supplements. As an example, some of them colonize the digestive tract at early stages of life and play a key role in the maturation of the immune system. Accordingly, a lack of implantation of these beneficial bacteria correlates with immune and inflammatory disorders, which constitute a growing health concern and are gradually understood, in the light of variations of the gut microbiota structure. Potential applications of probiotic bacteria further involve the treatment of diarrhoea caused by rotavirus, of allergy, of eczema, of irritable bowel syndrome and of inflammatory bowel diseases. The mechanisms underlying interactions between probiotic bacteria and the host thus constitute a hot topic.Surface molecules of probiotic bacteria play a central role in these interactions. Referred to as Microbe-associated Molecular Pattern (MAMP), these key molecules are recognized by corresponding pattern recognition receptors (PRR), present at the surface of the host cells. The role of MAMPs includes adhesion and modulation of the gut associated immune system, prior to that of the systemic immune system, by mediating a host/bacteria cross-talk. MAMPs include surface proteins, glycoproteins, lipoproteins, pilins, flagellins, as well as surface associated polysaccharides. Host PRRs, which can perceive MAMPs, include Toll-like receptors (TLR), as well as the C type lectin DC-specific intercellular adhesion molecule 3-grabbing non-integrin (DC-SIGN). They may be present at the surface of epithelial cells, and of dendritic cells.This oral presentation will illustrate the key role of probiotics’ MAMPs through examples of bifidobacteria, lactobacilli, and of propionibacteria. It will present textbook cases spanning from molecular to in vivo studies. Scientific data acquired during the last decade indeed place interactions between MAMP and PRR at the Centre of Probiotic/Host Interaction. The corresponding mechanisms are currently elucidated.