NAO can refer to:
- National Applications Office, an agent of the United States Department of Homeland Security
- National Audit Office in several nations
- National Academy Of Osteopathy, a Canadian based osteopathy college that teaches manual osteopathy in 62 cities across 32 countries
- Nautical Almanac Office in several nations
- New Age Outlaws, now known as Voodoo Kin Mafia in TNA Wrestling
- North Atlantic oscillation, a climatic phenomenon
- National Academy Orchestra of Canada, a Canadian orchestral training program located in Hamilton, Ontario
- National Academy of Opticianry
- nethack.alt.org, a server for the roguelike game NetHack
Nao can refer to:
- Nao (given name), a Japanese given name
- A three- or four-masted sailing ship used by the Portuguese and the Spanish all along the 15th century and early 16th. It was a close (and a bit smaller) relative of the carrack.
- Nao, the hero of the Aquablue comic
- Nao (singer), a Japanese singer who was the vocal of fripSide until 2009.
- Nao, the mascot of the Mabinogi network game.
- Nao (robot), a robot devised by the French company Aldebaran Robotics
- Nao (musical instrument)(鐃), traditional Chinese musical instrument, may refer to either an ancient bell or large cymbals
NaO can refer to:
- NaO Sodium oxide