T21, T.21 or T-21 may refer to : * 2C-T-21, a psychedelic phenethylamine of the 2C family * Junkers T 21, a manufacturer designation for the 1923 German Junkers Ju-21 reconnaissance aircraft * Limi-T 21, a popular merengue group from Puerto Rico * SJ T21, a 1950s Swedish diesel-hydraulic locomotive * Slingsby T.21, a 1944 British training glider * T21 Light Tank, a U.S. Army light tank design of World War II * T21 (rocket), a U.S. Army chemical warfare rocket of World War II * T-21 tank, 1937 Czechoslovak S-II-c tank prototype (known as the T-21 tank after 1939) * , an initiative by the Preventing Tobacco Addiction Foundation to raise the legal minimum sales age of tobacco to 21.