Intracellular pathogens are still responsible for many important public health problems. Their study as for extracellular pathogens allows to generate new tools for diagnostic, treatment or vaccines. But their intracellularity provides means to tackle host cell-specific mechanisms including signaling pathways, metabolism, cytoskeleton plasticity and many other aspects. Since 1986, how the intracellular bacterium Listeria monocytogenes survives in the environment and behaves during infection is the object of intense investigation. This bacterium is still responsible for severe food borne infections leading to gastroenteritis, meningitis and abortions, with a mortality rate of 30%. The recent epidemics in South Africa with ca. 200 deaths has demonstrated that epidemics can still occur and lead to an important number of deaths. The capacity of Listeria to produce an infection is due to its ability to cross three tight host body barriers: the intestinal barrier, the blood brain barrier, and the placental barrier. An arsenal of « virulence factors » allows Listeria to survive and persist in the intestinal lumen, to enter into cells and disseminate in the various tissues that it infects, exploiting cellular signaling pathways and components to its own profit. The talk will illustrate how investigating these various aspects have led to new concepts and changes in paradigms in several areas of biology. We will also present recent data, such as the interaction of Listeria with the gut microbiome and the role of several bacteriocins.