The 56^th International Mathematical Olympiad was held in Chiang Mai, Thailand, from 4 to 16 July 2015.

The IMO 2015 is hosted by The Institute for the Promotion of Teaching Science and Technology (IPST) · Chiang Mai University · The Mathematical Association of Thailand under the Patronage of His Majesty the King · The Promotion of Academic Olympiad and Development of Science Education Foundation under the Patronage of Her Royal Highness Princess Galyani Vadhana Krom Luang Naradhiwas Rajanagarindra (POSN). The International Mathematical Olympiad (IMO) is the World Championship Mathematics Competition for High School students and is held annually in a different country. The first IMO was held in 1959 in Romania, with 7 countries participating. Nowadays, there are over 100 countries participating from 5 continents.