The first IMO was held in Romania in 1959. Seven countries entered – Bulgaria, Czechoslovakia, East Germany, Hungary, Poland, Romania and the Soviet Union – with the hosts finishing as the top-ranked nation.[4] The number of participating countries has since risen: 14 countries took part in 1969, 50 in 1989, and 104 in 2009.[5]
North Korea is the only country whose entire team has been caught cheating, resulting in its disqualification at the 32nd IMO in 1991 and the 51st IMO in 2010.[6] (However, the 2010 case was controversial.[7][8]) There have been other disqualifications of contestants due to cheating, but such cases are not officially made public.[9] In January 2011, Google gave €1 million to the IMO organization to help cover the costs of the events from 2011 to 2015.[10]
^1991 marked the Soviet Union's last participation. From 1992, former Soviet Union countries – including Russia – entered separately.[11]
^At the time of the Olympiad, Hong Kong was under British colonial rule.
^Following the COVID-19 pandemic, the 2020 IMO was postponed from July to September hoping to keep the competition in-person. Then it was changed to a virtual event.[38]
^ abFor the two virtual IMOs, all problems were selected by the Problem Selection Committee instead of the Jury made up of all team leaders, and problems were sent to the team leaders shortly before the exams for translation. Each team took the IMO exam at a national exam centre, and starting times of all exams were in the interval between 07:30 and 12:00 UTC (both ends included) of each exam day. An IMO Commissioner of another nationality was present at each centre to oversee the whole exam, and the IMO Chief Invigilator monitored all exams using webcams.[39][40]
^The 2021 IMO was originally to be held in Washington D.C., US. The US gave up hosting after the COVID-19 pandemic had started.[43][38]
^ abUnofficial events were held in Finland and Luxembourg in 1980. "UK IMO register". IMO register. Archived from the original on 2001-10-16. Retrieved 2011-06-17.
^ ab"Virtual IMO 2020 – Russia". International Mathematical Olympiad Foundation. 2020-07-11. Archived from the original on 2023-06-09. Retrieved 2022-07-16.