The International Olympiad in Informatics (IOI) is an annual informatics competition for secondary school students. The first IOI was held in 1989.

The contest consists of two days computer programming, solving problems of an algorithmic nature. Students compete on an individual basis, with up to four students competing from each participating country (with around 81 countries in 2004). Students are selected through national computing contests. For example, in Britain, students compete in the BIO for a place in the national team.

On each of the two competition days, the students are typically given three problems which they have to solve in five hours. Each student works on his/her own, with only a computer and no other help allowed, specifically no communication with other contestants, books etc. Usually to solve a task the contestant has to write a computer program (in C, C++ or Pascal) and submit it before the five hour competition time ends. Later on, the program is graded by being run with secret test data, consisting of multiple (typically 10 or 20) test cases. The contestant is awarded points for each test case that his program solves correctly, and within the given time and memory limit. In some cases, the contestant's program has to interact with a secret computer library, which allows problems where the input is not fixed, but depends on the program's actions - for example in game problems. Another new type of problems has known inputs which are publicly available already during the five hours of the contest. For these, the contestants have to submit the according output file instead of a program, and it is up to them whether they obtain the output files by writing a program (possibly exploiting special characteristics of the input), or by hand, or by a combination of these means.

The scores from the two competition days and all problems are summed up separately for each contestant. At the awarding ceremony, contestants are awarded medals depending on their relative total score. The top 50% of the contestants (i.e. two per country, on average) are awarded medals, such that the relative number of gold : silver : bronze : no medal is approximately 1:2:3:6 (thus 1/12 contestants get a gold medal)

IOI 2009 will be held in Plovdiv, Bulgaria, 2009

IOI 2008 will be held in Alexandria, Egypt, 2008

IOI 2007 will be held in Zagreb, Croatia, 2007

IOI 2006 will be held in Mérida, Yucatán, Mexico, August 13 - 20, 2006

IOI 2005 was held in Nowy Sącz, Poland, August 18 - 25, 2005

IOI 2004 was held in Athens, Greece, September 11 - 18, 2004

IOI 2003 was held in Kenosha, Wisconsin, USA, August 16 - 23, 2003

IOI 2002 was held in Yong-In, Republic of Korea, August 18 - 25, 2002

IOI 2001 was held in Tampere, Finland, July 14 - 21, 2001

IOI 2000 was held in Beijing, People's Republic of China, September 23 - 30, 2000

IOI 1999 was held in Antalya-Belek, Turkey, October 9 - 16, 1999

IOI 1998 was held in Setúbal, Portugal, September 5 - 12, 1998

IOI 1997 was held in Cape Town, South Africa, November 30 - December 7, 1997

IOI 1996 was held in Veszprém, Hungary, July 25 - August 2, 1996

IOI 1995 was held in Eindhoven, The Netherlands, June 26 - July 3, 1995

IOI 1994 was held in Haninge, Sweden, July 3 - 10, 1994

IOI 1993 was held in Mendoza, Argentina, October 16 - 25, 1993

IOI 1992 was held in Bonn, Germany, July 11 - 21, 1992

IOI 1991 was held in Athens, Greece, May 19 - 25, 1991

IOI 1990 was held in Minsk, Belarusian SSR, Soviet Union, July 15 - 21, 1990

IOI 1989 was held in Pravetz, Bulgaria, May 16 - 19, 1989.