Au or AU may refer to:

In science

• Astronomical unit, the (approximate) distance between the Earth and the Sun
• Atomic units, a system of measurement units based on fundamental atomic properties
• Au, the chemical symbol of Gold

In computing

• .au Internet country code top-level domain for Australia
• au file format, Sun Microsystems' audio format
• Audio Units plug-in programming interface from Apple Computer

Organisations

• Adventure Unlimited
• African Union
• Allahabad University
• American University
• Americans United for Separation of Church and State
• Andrews University, located in Michigan, USA and affiliated with the Seventh-day Adventist Church
• Athabasca University
• au (mobile phone operator), of Japan
• Auburn University
• Austral Lineas Aereas (IATA airline code AU)

Places

• Australia (ISO country code); see AU for subdivisions
• Austria (obsolete NATO country code)

Miscellaneous

• Alternative universe (fan fiction), a fan fiction term
• Annals of Ulster, in Irish historical writings
• Au is a cartwheel (Capoeira) in the Brazilian martial art of Capoeira
• Au (區 or 歐) is a family name in Hong Kong

Au is an old Germanic word for rivulet, cognate of several rivers Aa and with Å in Swedish.

In geography

Germany:

• Au in der Hallertau
• Au-Breisgau

Switzerland:

• Au, Schaffhausen
• Au, Thurgau
• Au, Zürich

Austria:

• Au, Austria
• Au am Anzbach
• Au am Kraking
• Au am Leithaberge
• Au an der Donau
• Au an der Traun
• Au bei Brandstatt
• Au bei der Traun
• Au bei Ed
• Au bei Hischmannsberg
• Au bei hohen Steg
• Au bei Natternbach
• Au bei Sirfling
• Au bei Turnau

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