X21

X21 may refer to:

X.21, a telecommunications standard X21 (group), a Japanese girl idol group X21 (New York City bus) Northrop X-21, an experimental aircraft SA-X-21, a Russian anti-aircraft weapon system TGOJ X21, a Swedish electric multiple unit ThinkPad X21, a notebook computer Banham X21, a kit car from Banham Conversions