International Olympiad on Astronomy and Astrophysics (IOAA) is an annual event for highly performed high school students from all around the world. Established in Thailand 2006, it was initiated by five countries including Thailand, Indonesia, Iran, China and Poland with the aim to proliferate Astronomy among high school students, to foster friendship among young astronomers at international level so as to build cooperation in the field of Astronomy in the future among the young scholars.

Some of the countries which have ever hosted IOAA are Thailand in 2007, Indonesia in 2008, Iran in 2009, China in 2010, Poland in 2011, Brazil in 2012, Greece in 2013, Romania in 2014, Indonesia in 2015, India in 2016, Thailand in 2017, and China in 2018, Hungary will be hosting IOAA in 2019. 

The first president of IOAA is Assoc. Prof. Boonrucksar Soonthornthum and Assoc. Prof. Dr. Chatief Kunjaya from Indonesia as Secretary General. The election for the President and Secretary General is regularly conducted in 5 years term. After the election in India 2016, Dr. Gregorz Stachowski from Poland is currently enacting as President of the organization and Dr. Aniket Sule from India as the Secretary General for 2017 to 2021. 

The stages in the competition comprise of four exams: 

1. Theoretical Exam: consisting of 15 short questions and 2 or 3 long questions, with 5 hours to solve. It counts as 50% of the mark.
2. Data Analysis Exam: a paper- or computer-based task for analysing actual data obtained from professional astronomers, with usually 4 hours to solve. It counts as 25% of the mark.
3. Observational Exam: questions concerning direct observation of the sky (in the real sky or in a planetarium), recognizing stars, constellations, nebulae, great circles, etc. It counts as 25% of the mark.
4. Team Competition: A separated competition, in which national teams are set to do a huge task, involving both individual and group efforts, with theoretical and /or practical reasoning.

The first IOAA was held in the city of Chiang Mai, Thailand, from November 30 to December 9 of 2007, to commemorate the 80th anniversary of the King Bhumibol Adulyadej and the 84th anniversary of the Princess Galyani Vadhana. 21 countries which were Azerbaijan, Bangladesh, Belarus, Bolivia, Brazil, China, Greece, India, Indonesia, Iran, South Korea, Laos, Lithuania, Myanmar, Poland, Romania, Singapore, Slovakia, Sri Lanka, Thailand, and Ukraine participated the first IOAA. The international board also elected, for a five-year term, a President (Assoc. Prof. Boonrucksar Soonthornthum, Thailand) and a General Secretary (Assoc. Prof. Dr. Chatief Kunjaya, Indonesia). 

The second IOAA was held in 2008, August 19 to 28, in the city of Bandung, Indonesia, having the participation of 22 countries, including a team from Cambodia and an observer from Malaysia. 

The third IOAA was held in 2009, October 17 to 27, in the capital Tehran, Iran. The observational exam was held in the desert, in the Caravanserai of Deh Namak. 20 countries participated the competition including the first time participation for Kazakhstan and Serbia. 

The fourth IOAA was held in 2010, September 12 to 21, in the capital Beijing, China. One-hundred fourteen competitors attended, coming from 23 countries including the first time participation for Czech Republic, Philippines and Russia. 

The fifth IOAA was held in 2011, August 25 to September 4, around the cities of Katowice, Chorzow and Krakaw, Poland. This was the first IOAA held in Europe. The participants came from 26 countries, including the first time coming for Bulgaria, Colombia, Croatia, Hungary and Portugal. In Poland, the International Board elected a new President, Assoc. Prof. Dr. Chatief Kunjaya, Indonesia, and a General Secretary, Dr. Greg Stachowski, Poland. They also indicated two Regional Coordinators, (Dr. Thais Mothe Diniz, Brazil, for Americas and Dr. Aniket Sule, India, for Asia and Pacific) 

The sixth IOAA was held in 2012, August 4 to 13, at Rio de Janeiro and Vassouras, Brazil. The first time IOAA was held in South America. The participants came from 28 countries. 

The seventh IOAA was held from 27 July to 4 August 2013 in Volos, Greece. Total 39 teams from 35 countries participated in the event. These included first time for teams from USA, New Zealand, Canada, Malaysia, Armenia, Slovenia, Macedonia and Cyprus. 

The eighth IOAA was held from August 1 to 11, 2014 in Suceava and Gura Humorului, Romania. Total 42 teams from 37 countries participated in the event. These included first time for teams from Mexico, Pakistan, Nepal, Moldova and Montenegro. 

The ninth IOAA was held from 26th July to 4th August 2015. Total 46 teams from 41 countries participated in the event. These included first time teams from Estonia, Georgia, Kyrgyzstan and United Kingdom. In addition, observers from Sweden and Qatar attended the IOAA. 

The tenth IOAA was held in Bhubaneswar, India from December 9 to 19, 2016. Total of 48 teams from 42 countries participated in the event. 

The eleventh IOAA was held from 12 to 20 November 2017 at Thailand. Total 44 teams from 44 countries participated in the event.

The twelfth IOAA was held from 3 to 11 November 2018 at China. Total 45 teams from 39 countries participated in the event.