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

Transportation

Aviation

* Auster B.4, 1951 British light transport aircraft with rear ramp * B.A.C.H. Flugbetriebs IATA airline designator (ICAO BCF) * Bankair IATA code, ICAO airline designator (BKA) * Bensen B-4, Bensen Aircraft autogyro * Bäumer Sausewind, Bäumer B IV Sausewind, German 1920s sports aircraft * Flyglobespan IATA airline designator * Fokker F.11, Fokker B.IV, parent company's designation for American branch's F.11 seaplane * Hawker Hart, 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

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

In the military

Handpainted Wayzata soldier's flight bag back

* HMS B4, 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, SM ''UB-4'', a 1915 German U-boat * 203-mm howitzer M1931 (B-4), 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), ''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 (Dungeons & Dragons), The Lost City (B4), a ''Dungeons & Dragons'' adventure module

Other uses

* B4 (classification), a parasports classification for visually impaired athletes * B4 Championships, 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