The Gram-positive facultative intracellular bacterium Listeria monocytogenes is a model pathogen for elucidating important mechanisms of the immune response. Infection of mice with a sub-lethal dose of bacteria generates highly reproducible innate and adaptive immune responses, resulting in clearance of the bacteria and resistance to subsequent L. monocytogenes infection. Both the innate and adaptive immune systems are crucial to the recognition and elimination of this pathogen from the host.