Shortening the duration of treatment for patients with drug sensitive tuberculosis from 6 to 4 months has been attempted many times in clinical trials but thus far all have failed. These failures reveal our incomplete understanding of factors driving the need for such extensive treatments. Consistently, trials have demonstrated that 80-85% of patients are successfully cured after 4 months of therapy, including the extensive set of studies from the British Medical Research Council (BMRC) in the 1970s and 1980, the Tuberculosis Research Unit (TBRU) treatment shortening study in non-cavitary patients who achieve early culture conversion, and the more recent treatment shortening trials using fluoroquinolones like REMoxTB. The current standard of care is to over-treat all patients for a total of 6-months to avoid relapse in a small subset of patients at higher risk for incompletely understood reasons.