Amongst the methods available to diagnose a gastrointestinal infection, endoscopy offers the enormous advantage of allowing direct visualisation of the intestinal lumen and mucosa. It is also possible to take parietal biopsies and aspire samples of luminal liquid for further complementary tests. Except in the case of functional colonic disease, endoscopy allows diagnosis and prognosis and the establishment of adequate treatment. The author describes the various endoscopic techniques with their respective advantages and disadvantages.