XDR-TB is an acronym for extensively drug-resistant tuberculosis. One in three people worldwide is infected with latent tuberculosis bacteria (i.e., TB bacteria). It is only when these bacteria become active that people develop TB. The bacteria become active due to anything that can lower a person’s immunity, such as HIV, aging or certain medical conditions. TB can usually be treated with a regimen of four standard or first-line anti-TB drugs. If these drugs are misused or mismanaged, multidrug-resistant TB (MDR-TB) can develop. Treatment of multidrug-resistant TB with second-line drugs takes longer, is more expensive, and produces more side effects. Extensively drug-resistant TB can develop when these second-line drugs are also misused or mismanaged and therefore also become ineffective. Treatment regimens are severely limited by the resistance of extensively drug-resistant TB to first- and second-line drugs. Therefore, it is critical to properly manage TB control.