Inflammatory Bowel Disease (IBD) is an abnormal inflammatory response to an unknown trigger. Genetic studies have shown that patients with IBD may have a genetic predisposition to this condition. Further, it also appears that IBD patients have an abnormal immune response against intestinal microbiota. In this presentation, Dr Ken Croitoru walks through the evidence from studies suggesting that the abnormal inflammatory response in IBD patients is due, in part, to genetic alterations in the normal homeostatic processes that regulate host interactions with the normal gut microbes. With the discovery of pathogen recognition receptors [eg, toll-like receptors (TLR) and nucleotide-binding oligomerization domain receptors (NLR)], a paradigm shift has occurred. There is now a greater understanding of the immune cell responses to microbes and the roles these may have in IBD pathogenesis.