Clinical antibiotic therapy often fails. This is often due to "resistance", the ability of a bacterium to grow in the presence of antibiotics. However, non-resistant bacteria can also be "tolerant", i.e. they do not die in the presence of antibiotics. While antibiotic tolerance clearly delays sterilization of bacterial cultures in lab environments, its impact on clinical treatment outcome is unknown. Here, we seek to address this question by evaluating tolerance assays, establishing in vivo tolerance models, and describing molecular mechanisms underlying tolerance. These data will be invaluable in catalyzing the design of a prospective clinical study correlating antibiotic tolerance with patient outcomes.