This fourth edition of the WHO Guidelines for surveillance of drug resistance in tuberculosis presents up-to-date guidance on the design and implementation of setting-specific surveys and surveillance systems to measure the burden and trends of drug-resistant tuberculosis. The guidelines address recent advancements in drug susceptibility testing, including testing for second-line drugs and the use of rapid diagnostics. The document also presents strengthened guidance on data management and analysis, ethical considerations in surveys and surveillance of drug resistance, and investigation of associations between anti-tuberculosis drug resistance and HIV-infection and other risk factors.