A3

A3, A03 or A.III may refer to:

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

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

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

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

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
SP&S Class A3, a 1914 steam locomotives class

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

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
Comet A3 also known as C/2023 A3 (Tsuchinshan–ATLAS)
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.