Crohn's disease (CD), a chronic inflammatory process in intestinal segments leads to tissue damage. More than two thirds of CD patients need intestinal resection. Symptomatic clinical recurrence occurs in 60% by 10 years. The principal factors affecting postoperative recurrence are active smoking, penetrating disease, perianal lesions history, prior intestinal resection, small bowel resection extent, and prophylaxis treatment absence. Ileocolonoscopy within one year of surgery can predict clinical recurrence risk. Different therapies are proposed after surgery, to prevent post-operative recurrence : Thiopurines, 6-mercaptopurine (positive for clinical and endoscopic postoperative recurrence prevention), Anti-tumour necrosis factor therapy (anti-TNF), the most effective therapy. Intestinal microbiota acts as a central factor in the CD pathogenesis, and fecal stream role is clearly shown. Various changes in luminal flora with a possible link to local inflammation was also demonstrated. Bacteria associated with postoperative recurrence could be more pathogenic as adherent invasive E coli (AIEC), which could be a pathogen in CD through several mechanisms including increased mucosal colonization, adherence, replication and induction of TNF secretion. Alternatively, postoperative CD recurrence could be linked to a protective commensal species lack, such as Faecalibacterium prausnitzii. Microscopic inflammation occurs as early as 8 days after anastomosis in the neoterminal ileum mucosa. IL6, IL10 and TGFb levels, measured in neoterminal ileum early after surgery are associated with different rates of postoperative recurrence. It suggests cytokines implication in postoperative recurrence. T cells are major players in the intestinal immune response. The presence at time of surgery and persistence of disease inducing T cell clonal expansions could play an important role in post-operative recurrence. The main objective is to define a classification of ileal Crohn's Disease based on data integration on a large cohort of patients.