IAU may refer to:
- Immersion gold plating (IAu), a surface finish process in PCB manufacturing
- International Astronomical Union
- International American University
- International American University College of Medicine
- International Association of Universities
- International Association of Ultrarunners (IAU) is the governing body for ultra running
- Islamic American University
- Islamic Azad University
- Italian Actors Union, former name of the Guild of Italian American Actors, United States
- 5000 IAU, an asteroid
- Is Anyone Up?
- International Crossbow Shooting Union or International Armbrustschützen Union (IAU)
- Interamerican University of Puerto Rico
Iau is:
- The Iau language
- An occasional spelling for Eiao