PURPOSE OF REVIEW: The aim of this review is to report recent findings regarding the role of the gut microbiota in inflammatory bowel disease pathogenesis. RECENT FINDINGS: After a description of the current knowledge on inflammatory bowel diseases-associated dysbiosis, we will focus on the recent functional studies that analyzed the cross relationship between the gut microbiota and the host. SUMMARY: Recently published studies have provided an insight into the altered dialog between the intestinal microbiota and the host leading to gut inflammation. Further investigation will allow identifying new therapeutic targets either in the microbiota or the host.