F21

F21 or F-21 may refer to :

Aviation

 * F 21 Luleå, a Swedish Air Force wing
 * IAI F-21 Kfir, a 1973 Israeli-built all-weather, multi-role combat aircraft
 * Lockheed Martin F-21, a variant of the F-16 designed for the Indian Air Force
 * KAI KF-21 Boramae, a South Korean/Indonesian stealth fighter currently under development
 * Farman F.21 Moustique II, a French interwar airplane
 * Taylorcraft F-21, an American light aircraft

Nautical

 * F21 (torpedo), a torpedo developed for the French Navy
 * HMS Punjabi (F21), a 1937 British Royal Navy Tribal-class destroyer
 * ARV Mariscal Sucre, a Venezuelan navy frigate
 * INS Gomati (F21), an Indian Navy Godavari-class frigate
 * ROCS Tai Kang, a Taiwanese navy destroyer

Land transport

 * F-21 (Michigan county highway)
 * BMW Series 1, that had a model code called "F21"

Other uses

 * Schizotypal personality disorder, whose ICD-10 code is "F21"
 * Fluorine-21 (F-21 or 21F), an isotope of fluorine