B4

B4, B04, B.IV or B-4 may refer to:

Aviation

 * B4, IATA code of Beond, an airline based in Malé, Maldives
 * B4, IATA code of B.A.C.H. Flugbetrieb, an Austrian charter airline (ICAO code BCF)
 * B4, IATA code of Bankair, an US American charter airline (ICAO code BKA)
 * B4, then-IATA code of Flyglobespan, a former British airline
 * Auster B.4, 1951 British light transport aircraft with rear ramp
 * Bensen B-4, Bensen Aircraft autogyro
 * Bäumer B IV Sausewind, German 1920s sports aircraft
 * Fokker B.IV, parent company's designation for American branch's F.11 seaplane
 * Hawker B 4, Swedish designation for Hawker Hart biplane
 * Keystone B-4, United States biplane bomber
 * Lohner B.IV, an Austro-Hungarian World War 1 reconnaissance biplane
 * Pilatus B-4, Swiss glider also designated PC-11.

Locomotives

 * Alsace-Lorraine B 4, an Alsace-Lorraine P 1 class steam locomotive
 * Bavarian B IV, an 1852 German steam locomotive
 * GSR Class B4, a former Cork, Bandon and South Coast Railway steam locomotive of the Great Southern Railways, Ireland
 * LSWR B4 class, an 1891 British dock tank locomotive
 * PRR B4, an American Pennsylvania Railroad steam locomotive
 * Soo Line B-4 class, an American 0-6-0 steam locomotive
 * LB&SCR B4 class, a British tender locomotive class
 * LNER Class B4, a British class of locomotives

Automotive uses

 * Subaru B4, the name under which the Subaru Legacy is marketed in Israel
 * B4 (New York City bus), serving Brooklyn
 * B4 road (Namibia)
 * Bundesstraße 4, federal highway in Germany
 * Alpina B4, a German sports executive car

In the military

 * HMS B4, a British B-class submarine of the Royal Navy
 * Keystone B-4, a United States Army Air Corps biplane bomber
 * SM UB-4, a 1915 German U-boat
 * 203-mm howitzer M1931 (B-4, "Stalins Hammer"), a World War II Soviet ordnance piece
 * B-4 a US Air Force/USAAF flight bag
 * A level of vehicle armour

In science

 * Leukotriene B4 receptor and Leukotriene B4 receptor 2, two human genes
 * Lipoxin B4, a lipoxin
 * Proanthocyanidin B4, a B type proanthocyanidin
 * Vitamin B4, an alternate name for adenine
 * A stellar classification

In entertainment

 * B4 (music show), a defunct British music video show broadcast on Channel 4
 * B4 (TV channel), a defunct British music television channel
 * B-4 (Star Trek), an android in the Star Trek fictional universe
 * Babylon 4 space station, predecessor to Babylon 5 from the Babylon 5 television series
 * The Lost City (B4), a Dungeons & Dragons adventure module

Other uses

 * B4 (classification), a parasports classification for visually impaired athletes
 * B4 Street Fighter Championships, a 2000 fighting game tournament
 * B4 or B4 II, a Native Instruments virtual synthesizer for Hammond organ (B-3) sound emulation
 * B4-mount, used for professional video cameras such as Betacam
 * An international standard paper size (250×353 mm), defined in ISO 216
 * B04, Alekhine's Defence chess code
 * 1. b4, Sokolsky Opening in chess