B21

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

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

• 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

• 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

• B. 21 ({{langx|cs|link=no|Král a uhlíř||King and Collier}}), a Czech comic opera by Dvorak
• B21 (band), a British bhangra group

• 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

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• Must B 21, a 2003 album by American singer will.i.am
• 21B (disambiguation)

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