Aa or AA may stand for:

Aa

• Aa, a genus of orchid.
• an alternative transcription of Å, a letter in the Swedish, Norwegian, Danish, and other alphabets.
• a river in northern France: Aa River, France.
• one of several Aa Rivers (or rather a stream / creek) in Scandinavia, Germany, Switzerland and the Netherlands . Aa can be a transcription of Å: see below and Å (disambiguation).
• a type of basaltic rock, pronounced "ah-ah", usually dark-colored with a jagged surface, formed in large sheets from slow-moving lava. It is one of two chief forms of rock emitted from volcanoes of the Hawaiian type, the other being pahoehoe.
• a village on northern coast of Estonia.

AA

• AA ("double A"), one of the standard sizes for dry cell batteries
• AA ("double-A") is a league level in minor league baseball
• Ace-Ace (in Poker)
• Alcoa stock symbol
• Alcoholics Anonymous
• American Airlines
• American Atheists
• America's Army, a computer game (FPS) made by the US Army
• Ann Arbor Railroad (AAR reporting mark AA)
• Anti-Aircraft
• Anti-Aliasing, A computer graphics term meaning "the technique of minimizing aliasing when representing a high-resolution signal at a lower resolution."
• Argentinum Astrum
• ASCII Art or Shift-JIS art
• Associate of Arts or Associate in Arts
• Authentication and Authorization
• Automobile Association, a British motoring organisation
• The postal abbreviation for United States armed forces in the Americas (excluding Canada).
• Aerolineas Argentinas: Argentinian Airline.

aa

• Afar language (ISO 639 alpha-2, aa)