A3

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, 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 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 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 class designed by Sir Nigel Gresley
 * Prussian A 3, a 1910 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, a British A-class submarine of the Royal Navy
 * 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 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), 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
 * 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
 * Zeolite A-3, a potassium-type molecular sieve also known as 3A.