Over the past decade, an expanding repertoire of health disorders in humans has been associated with aberrations in the gut microbiota composition (called dysbiosis). The precise role of the microbiota in these disorders remains largely unclear although it appears that potentially pathogenic members of the human gut microbiota can contribu to the pathophysiology of inflammatory bowel disease (IBD) and, in contrast, some other beneficial members have been identified as sensors of good The impact of the microbiota goes beyond immune-mediated diseases and in mice and susceptibility to infection, processes of dietary energy extraction and fat storage, and even behavior have been Nature to be modified by microbiota guly special of Immunology). There is also growing interest in the ability of the gut microbiome to influence host functions within and beyond the gastrointestinal tract.