The intracellular bacterium Listeria monocytogenes continues to serve as a model to define general paradigms of cell-mediated immunity. Genetic manipulations of the bacterium and its murine host have allowed us to begin dissecting the intricate interactions between this bacterium and the immune system. As a result, we have gained new insights into the mechanisms of immune surveillance, achieved better understanding of bacterial tactics for immune evasion and developed novel strategies in vaccine development.