Crohn's disease and ulcerative colitis are chronic inflammatory bowel diseases characterized by recurring active inflammation of the digestive tract. Ulcerative colitis and Crohn's disease are complex diseases involving genetic as well as environmental factors. Since the introduction of genome-wide association studies, enormous progress has been made in recent years in unravelling the genetic basis of these diseases. Up till now, more than 30 associated genes have been identified for Crohn's disease and more than 10 for ulcerative colitis. Results of genome-wide association studies have increased knowledge about the pathogenesis of chronic inflammatory bowel disease. Understanding of the molecular basis of inflammatory bowel disease may lead to new therapeutic options. Thanks to recent developments, genetic research is likely to become instrumental in future diagnostics and treatments for inflammatory bowel disease.