The World Health Organization published its first catalogue of mutations in M. tuberculosis known to be associated with resistance to a range of antibiotics in June 2021. This paper, just published in Lancet Microbe, describes in detail how the catalogue was constructed and its effectiveness, as measured by sensitivity and specificity. The CRyPTIC consortium not only contributed the majority of the samples used, but all the raw genetic files were processed through the pipeline created by CRyPTIC and CRyPTIC members helped with the analysis and interpretation.