AAR or Aar may refer to:

• AAR Corporation, an American aviation engineering company
• "Air-to-air refueling", also known as aerial refueling, the practice of transferring fuel from one aircraft to another during flight
• AAR, IATA airport code for Aarhus Airport in Tirstrup, Denmark
• AAR, ICAO airline code for Asiana Airlines of South Korea

The Aare or Aar is a tributary of the High Rhine and the longest river that both rises and ends entirely within Switzerland.

Age at Risk (AaR) is a time-based risk measure designed to measure longevity risk in actuarial models.