B21

B21 may refer to:

Places

 * Kepong–Selayang Highway (Selangor state route B21), Malaysia
 * Autovía B-21, Spain; a motorway
 * Harumi Chūō (station code ), Tokyo BRT, Tokyo, Japan
 * Mikamo Station (station code ), Higashimiyoshi, Miyoshi, Tokushima, Japan; a train station
 * Shin-Hōsono Station (station code ), Seika, Kyoto, Japan; a train station
 * Sugarloaf Regional Airport (FAA airport code ), Franklin County, Maine, USA

Transportation and vehicular

 * B21 (New York City bus), a bus route serving Brooklyn, New York City, New York State, USA
 * Unterseeboot B-21, a WW1 German submarine

Automotive

 * BSA B21 (1937–1939), a British motorcycle made by Birmingham Small Arms Company, Birmingham, England
 * Leyland B21 (1979–1985), a bus chassis manufactured by Leyland
 * Volvo Redblock Engine (B21), an automotive engine
 * Chevron B21, a racing prototype Group 5 sports car built by Chevron Cars Ltd

Aviation

 * Northrop Grumman B-21 Raider, a 21st-century American stealth bomber
 * North American XB-21 ("B-21"), an experimental bomber aircraft developed in the late 1930s
 * B.21/35, British interwar twin-engined bomber

Arts, entertainment, media

 * B. 21 (Král a uhlíř), a Czech comic opera by Dvorak
 * B21 (band), a British bhangra group

Other uses

 * B-21 (machine), a cypher machine invented by Boris Hagelin
 * Burroughs B21, a variant of the Burroughs B20 microcomputer
 * HLA-B21, an HLA - B serotype
 * Boron-21 (B-21 or 21B), an isotope of boron
 * B21, a nuclear reactor at Dungeness nuclear power stations, Dungeness headland, southern Kent, England, UK