The mechanisms underlying the chronic intestinal inflammation that is a hallmark of inflammatory bowel diseases (IBD) are complex. Components of the pathological response include the adaptive and innate immune systems, as well as the intestinal epithelium and endothelium. Advances in the understanding of the roles of each of these components have resulted in the development of multiple biological agents that all represent an alternative to the use of current therapies in patients with refractory Crohn's disease or ulcerative colitis. This study systematically reviews the mechanisms of action, efficacy and safety of new and emerging therapies that are currently in clinical trials and discusses future directions in the treatment of IBD.