Crohn's disease (CD) and ulcerative colitis (UC) are the two major forms of inflammatory bowel disease (IBD). Although their etiology is still unknown, the pathogenic mechanisms underlying intestinal inflammation have made impressive progress in our understanding. In particular, the abnormalities underlying IBD pathogenesis are not restricted to those mediated by classical immune cells such as T and B lymphocytes, macrophages and dendritic cells, but also nonimmune cells. Interestingly, endothelium has become one of the major areas of investigation in gut inflammation.