Substantial progress has been made in the last years in characterizing the susceptibility genes involved in IBD pathogenesis, especially for Crohn's disease. Although some genetic factors associated with Crohn's disease also predispose individuals to ulcerative colitis, markers specific only for ulcerative colitis have been found. Recent genome-wide association studies in ulcerative colitis have identified several new loci, and suggested many new potential pathways. The identified susceptibility genes and their variants could be useful to predict disease course and to improve stratification of patients, when correlated with other subphenotypes. Moreover, understanding the biological pathways involved in the disease could lead to the development of new treatments and molecules that specifically target such pathways, discover different therapeutic approaches and eventually progress to personalized treatment.