TB is the most prevalent infection in the world. The emergence of the HIV epidemic has dramatically increased the risk of developing clinical TB in infected persons, substantially increasing TB rates globally. Preventive therapy with INH for 6 to 12 months substantially reduces the risk of developing clinical TB in persons with tuberculous infection. Yet, preventive therapy is not fully used because of lack of knowledge about TB among health care professionals, patient nonadherence with preventive therapy regimens, and drug toxicity. Persons at high risk for developing TB should be screened for infection with a tuberculin skin test and given preventive therapy when appropriate. Promising new regimens of shorter duration and new drug delivery systems are currently being evaluated. Preventive therapy must be widely adopted if the goals of TB control and eventual elimination are to be achieved.