A21

A21, A-21 or A.21 may refer to:

• A21 Cocktail Lounge, acclaimed to be one of the world´s best bars
• a21, Inc., a United States company
• A-21 water-alcohol-fuel emulsion developed by American inventor Rudolf W. Gunnerman
• Aero A.21, a 1920s-era Czechoslovakian military aeroplane
• Arrows A21, a Formula One car
• British NVC community A21 (Ranunculus baudotii community), a plant community
• Focke-Wulf A 21, a photographic survey variant of the 1927 German Focke-Wulf A 17
• Stearman XA-21 twin engined United States attack bomber

and also:

• One of the Encyclopaedia of Chess Openings codes for the English Opening in chess

For roads numbered as A21, see List of A21 roads.