H21
# H21

H21 or H-21 may refer to:

* British NVC community H21, a type of heath community in the British National Vegetation Classification
* Highway H21 (Ukraine)
* HMS H21, a Royal Navy H-class submarine
* HMS Scimitar (H21), a Royal Navy S-class destroyer
* Mata Hari (1876–1917), German spy code named H-21
* Piasecki H-21, an American helicopter
* Institute H21, a Czech think tank that created the website Prezident 21
