The IMO, an annual mathematics competition for high school students, is the oldest of the international science olympiads. About 80 countries send teams of (at most) six students each. The examination is held over two consecutive days; the contestants have four-and-a-half hours to solve three problems on each day. The problems chosen are from various areas of secondary school mathematics, broadly classifiable as geometry, number theory, algebra, and combinatorics. Teams are not officially recognized; all scores are given only to individual contestants.

The official IMO web site is www.imo-official.org, but the Wikipedia entry (below) provides more information about the format and history of the competition.