T21 may refer to:

Aircraft Junkers T.21, a German reconnaissance aircraft produced in the Soviet Union Slingsby T.21, a British training glider

Rail and transit Minami-morimachi Station, in Kita-ku, Osaka, Japan Myōden Station, in Ichikawa, Chiba, Japan SJ T21, a Swedish locomotive Yakuriguchi Station, in Takamatsu, Kagawa Prefecture, Japan

Ships and boats , a tank landing ship of the Venezuelan Navy

Mistral T-21, a Canadian sailboat

Other uses T21 (rocket), an American chemical warfare rocket Down syndrome, or trisomy 21 Estonian national road 21 T21 road (Tanzania) T21 Light Tank, an American light tank

ThinkPad T21, a notebook computer Trisomie 21, a French cold wave group