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.
Website: http://olympiads.win.tue.nl/ioi/