A3, A03 or A.III may refer to: * A3 paper, a paper size defined by ISO 216

Biology

* A3 regulatory sequence, a sequence for the insulin gene * Adenosine A3 receptor, Adenosine A₃ receptor, a human gene * Annexin A3, a human gene * ATC code A03 ''Drugs for functional gastrointestinal disorders'', a subgroup of the Anatomical Therapeutic Chemical Classification System * Brachydactyly type A3, a disease * British NVC community A3 (Spirodela polyrhiza - Hydrocharis morsus-ranae community), a British Isles plants community * Gibberellin A3, a plant hormone * HLA-A3, a Human MHC Serotype HLA-A * Subfamily A3, a rhodopsin-like receptors subfamily * Urea transporter A3, a trans-membrane protein

Games

* ''A3!'', a Japanese video game and multimedia franchise * A3 - Assault on the Aerie of the Slave Lords, a 1981 module for the Dungeons & Dragons fantasy role-playing game * Alpha Trion, as the former name of this character from the Transformers Series * Bird's Opening (A03), in chess, by the Encyclopaedia of Chess Openings code

Music

* A3, a musical note, the A below Middle C * Alabama 3, a band known as A3 in the U.S. to avoid confusion with the country group Alabama * A-3, a List of Yamaha products#Electronic musical instruments, Yamaha musical instrument product

Sports

* A3 (classification), an amputee sport classification * A3 Champions Cup, a club football tournament also known as the East Asian Champions Cup * Arrows A3, a 1980 racing car * A3, a grade (climbing), climbing grade

Vehicles

* A-3 lifeboat, a 1947 lifeboat for carrying by the SB-29 Superfortress * Abrial A-3 Oricou, a French touring aircraft designed in 1927 * Audi A3, a model of automobile * Aussat (Optus) A3, a 1987 Australian telecommunication satellite * Bavarian A III, an 1851 German steam locomotive model * Chery A3, a compact car * LNER Gresley Classes A1 and A3, a Pacific Locomotive Designed by Sir Nigel Gresley * Prussian A 3, a 1910 List of Prussian locomotives and railbuses#Railbuses, Prussian railbus * SP&S Class A3, a 1914 steam locomotives class

Weapons and military

* A-3 Falcon, a variant of the Curtiss Falcon, an attack aircraft manufactured by the Curtiss Aircraft Company * A-3 Skywarrior, a strategic bomber manufactured by Douglas Aircraft Company * AUG A3, a variant of the Austrian Steyr AUG rifle * Fokker A.III, a 1915 armed version of the Fokker M.5 aircraft * HMS A3, HMS ''A3'', a British A-class submarine of the Royal Navy * Kampfgeschwader 200, ''Kampfgeschwader'' 200, from its historic ''Geschwaderkennung'' code with the Luftwaffe in World War II * Polaris A-3 missile, an American submarine-launched missile * Wendes Artillery Regiment, a former Swedish Army artillery regiment, by designation * A3, the Continental Staff System, staff designation for air force headquarters staff concerned with operations ** A3 Air Operations Branch, of the Joint Force Air Component Headquarters UK * USS Grampus (SS-4), USS ''Grampus'' (SS-4), a ''Plunger''-class submarine of the United States Navy * Aggregate 3, the 3rd design in the Aggregate family of rockets, precursor to the V-2 rocket, developed by the Germans during World War II

Other uses

* A₃, an example of a root system with numerous physical and geometrical applications * A-3 visa, a document given to employees of A-1 and A-2 Visa Holders who are representing a foreign government inside the U.S. * A3, the code for permission to use specific land or premises for restaurants and cafés in town and country planning in the United Kingdom * A3 roads, in several countries * A-003, the fourth abort test of the Apollo spacecraft * Biu-Mandara A.3 languages, an Afro-Asiatic family of languages spoken in Cameroon and Nigeria * Cowon A3, an audio media player * Aegean Airlines, by IATA code * Tonga, by aircraft registration code * ARITH-MATIC, as the former name for this programming language * "Agora! Anarchy! Action!", a slogan for Agorism taken from the ''New Libertarian Manifesto'' by Samuel Edward Konkin III * A3 problem solving, a structured problem solving and continuous improvement approach, first employed at Toyota * Samsung Galaxy A3, a smartphone manufactured by Samsung Electronics * Samsung Galaxy A03, a smartphone manufactured by Samsung Electronics * Airbus A³ Vahana, A³ (A-cubed), an Airbus start-up in the Silicon Valley * A3 (TV channel), an Algerian public national television channel also known as Thalitha TV * RED A03, an aircraft diesel engine by German company Red Aviation GmbH