AOU

AOU may refer to:


 * American Ornithological Society, formerly the American Ornithologists' Union
 * Apparent oxygen utilisation
 * Arab Open University, private university
 * Aou (trigraph)
 * Age of Ultron, a 2013 series published by Marvel Comics
 * Avengers: Age of Ultron, a 2015 superhero film of the same name by Marvel Studios