Tuberculosis is recognized as the world's leading bacterial cause of death. Yet 95% of infection is believed to exist in an asymptomatic 'latent' form that is defined not by the identification of bacteria, but by the host immune response in the form of reactivity to tuberculosis proteins in the tuberculin skin test. It seems likely that clinically defined latent tuberculosis actually represents a spectrum that runs from elimination of live bacilli to subclinical disease: hence, it might be unhelpful to use a single term to describe all these conditions. To support this view, here we focus on recent increased understanding of the heterogeneity in both bacillary physiology and host immune response that potentially illuminates new therapeutic and diagnostic approaches to this condition.