C-21

C-21, C 21, or C21 may mean:

* C21, a boy band from Denmark
* C-21 Dolphin, a flying boat used by the United States Army Air Corps
* HMS C21, a 1909 British C class submarine
* Learjet C-21, a United States military version of the Learjet 35A
* Sauber C21, a 2002 racing car
* Space Adventures C-21, a Myasishchev Design Bureau created design for a suborbital rocketplane for Space Adventures

and also :
* Century 21
* Anal cancer ICD-10 code