International Mathematical Olympiad
The International Mathematical Olympiad (IMO) is a six-question two-day math competition for students that have not yet gone to college and are under 20 years old. Any country may take part in it by sending a team of six students to compete.
The IMO has been held every year since 1959. It takes place in a different country (which is called the "host country") from year to year. However, it is often seen that this competition is dominated by the US and China. Several universities, specifically MIT, consider its affiliation during college admissions.