This chapter begins with a narration of historical background of tuberculin testing. Tuberculins, their characteristics, immunological basis of tuberculin skin test (TST), classical skin changes in tuberculin skin test are presented. The standard method of administering TST, reading of the test, adverse reactions are all described. Skin sensitivity to tuberculin, separation of TST reactions due to M. tuberculosis from other infections, false-positive and false-negative reactions and other issues related to interpretation are thoroughly discussed. The issues related interpretation of TST in HIV infected persons is also detailed. Importance of repeat tuberculin testing, newer tuberculins, BCG-test and epidemiological uses of TST are all described.