Abstract : Over the past 10 years, the "Pathogénie Microbienne Moléculaire" unit of Professor Philippe Sansonetti has studied the molecular cross talk between the intestinal micro-biota and the gut epithelium, aiming to better understand how this mutualistic symbi-osis delineates homoeostasis and, when perturbed, prompts pathology. To do so, the unit has manipulated both bacterial and epithelial cells, and used cutting-edge technology. More recently, the lab has turned its focus also on studying the intestinal crypt and more specifically the intestinal stem cell for their role in epithelial regener-ation and long-term epithelium renewal. Here, we provide a brief review summarising recent results obtained from the lab, with particular focus on the intestinal crypt.