Only to a small extent have the underlying causes of Crohn’s disease and ulcerative colitis been revealed so far. This is a major obstacle for a fundamental improvement of diagnostic and therapeutic approaches. Recent findings presented by Prof. Dirk Haller (Technische Universität München, Munich, Germany) at the Gut Microbiota for Health World Summit that took place in Barcelona, March 14-15, 2015, give reason to hope that this situation might be overcome in the near future. One key to the solution is the gut microbiota composition.