Inflammatory Bowel Disease, Crohn's disease and ulcerative colitis, are complex, multifactorial, polygenic diseases. Huge progresses in the knowledge of human genome and genotyping techniques have allowed the identifications of dozens of genes and loci associated with these diseases. These discoveries set the path for a new molecular classification of these diseases and let us see new therapeutic possibilities. The present paper highlights, in the setting of the Synthèse CHU 2009 meeting, the contributions of the team of the CHU and university of Liège in this field.