The author presents a brief review of the main pathophysiological hypotheses put forward to explain the formation of lesions of inflammatory bowel diseases (ulcerative colitis and Crohn's disease). No infectious or alimentary cause has been found. Immunological abnormalities are numerous, but none of them seems to be primary. The effector role of inflammation mediators is better known and leads to new developments in therapeutics. The study of healthy relatives is an interesting means of looking for abnormalities that pre-exist the disease, as seems to be the case with intestinal permeability. The french contribution of fundamental research on inflammatory bowel diseases is insufficient and must be stimulated.