Au, AU or au may refer to:

• Absorbance Units, a reporting unit in spectroscopy
• Astronomical unit, the average distance between the Earth and the Sun (roughly speaking)
• Atomic units, a system of units convenient for atomic physics and other fields
• Gold, a chemical element with the symbol Au
• Arbitrary unit, a relative placeholder unit for when the actual value of a measurement is unknown or unimportant

.au is the Internet country code top-level domain (ccTLD) for Australia.

Ankara University is a public university in Ankara, the capital city of Turkey. It was the first higher education institution founded in the Turkish Republic.

Åbo Underrättelser is a Swedish language newspaper published in Finland, published Tuesday through Saturday. Its headquarters are located in Turku (Åbo in Swedish). Åbo Underrättelser holds the distinction of being the oldest newspaper still in print in Finland, having been founded by Christian Ludvig Hjelt in 1823 (the first edition being published on January 3, 1824).
The newspaper's primary readership consists of Swedish-speakers in Turku and Åboland. Its circulation is 7,562.