# A3

A3, A03 or A.III may refer to:

## Biology

* A3 regulatory sequence, a sequence for the insulin gene
* Adenosine A$_3$ 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
* 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

* A$_3$, 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.