A3 can refer to:

• A3, a paper size defined by ISO 216.
• A3 (Switzerland), a motorway connecting Basel to Sargens
• A3 road (England), a trunk road connecting London to Portsmouth
• A3 freeway (Romania), a freeway, currently in construction, linking Transylvania to Bucharest
• A3 Motorway (Italy), connecting Naples to Reggio Calabria
• A3, a German rocket design during World War II
• Alien Adopt Agency, an online game
• Alabama 3, as the United States alias of the London band
• Audi A3, a brand of automobile
• Bundesautobahn 3 (Germany), an autobahn connecting Wesel to Passau
• HMS A3, a British A class submarine of the Royal Navy
• USS Grampus (SS-4), a Plunger class submarine of the United States Navy
• In town and country planning in the UK, A3 is the code for permission to use specific land or premises for restaurants and cafés.

The variant A-3 can refer to: There have been many standard sizes of paper at different times and in different countries. ... ISO 216 specifies international standard (ISO) paper sizes, used in most countries in the world today. ... The A3 motorway The A3 is a motorway in Switzerland. ... The A3 near Liphook The A3 is a trunk road in Southern England, connecting London to Portsmouth. ... The project of the A3 motorway is rather new comparing to the other infrastructure projects in Romania. ... The A3 Motorway is a toll-free road in the south of Italy, going from Naples to Salerno and then from Salerno to Reggio di Calabria. ... The Aggregate series was a set of rocket designs developed in 1933–1945 by a research program of Nazi Germanys army. ... Alien Adoption Agency (A3: Awakening), also known as AAA or A3, is a massive on-line game and community, which has been running since 1997 created by Linear Horizons, LLC. The game is an online battle simulation/strategy game based on a multiplayer text-based game about aliens with a... Alabama 3 is an psychobilly trip hop band from Brixton, England, a suburb of London. ... The A3 is a compact luxury car built by Audi since 1996. ... Map of the A 3 in Germany Bundesautobahn 3 (BAB 3 or A 3) is an German Autobahn that links the border to the Netherlands near Wesel in the northwest to the Austrian border near Passau in the southeast. ... HMS A3 was an early Royal Navy submarine. ... The A class was the Royal Navys first class of British-designed submarines. ... The Royal Navy of the United Kingdom is the senior service of the British armed services, being the oldest of its three branches. ... USS Grampus (SS-4), a Plunger-class submarine torpedo boat later named A-3, was the fourth ship of the United States Navy to be named for two members of the dolphin family (Delphinidae): Grampus griseus, also known as Rissos Dolphin, and Orcinus orca, also known as the Killer... The Plunger-class was an early class of United States Navy submarines, used primarily during World War I. General Characteristics Lead Boat: USS Plunger (SS-2) Builders: Crescent Shipyard (SS 2, 3, 5, 7, 8), Union Iron Works (SS 4, 6) Number of boats: 7 boats Displacement: 107 tons Length... The United States Navy (USN) is the branch of the United States armed forces responsible for naval operations. ... Town and Country Planning is the system by which the British government seeks to maintain a balance between economic development and environmental quality in England. ...

• A-3 Skywarrior, a strategic bomber manufactured by Douglas Aircraft Company
• Alpha Trion, as the former name of this character from the Transformers Series
• ARITH-MATIC, as the former name for this programming language