The International Science Olympiads are a group of worldwide annual competitions in various areas of science. The competitions are designed for the 4-6 best high school students from each participating country selected through internal National Science Olympiads, with the exception of the IOL, which allows two teams per country, the IOI, which allows two teams from the hosting country, and the IJSO, which is designed for junior secondary students. Early editions of the Olympiads were limited to the Eastern Bloc, but later they gradually spread to other countries. There are 12 international science olympiads to date:
The Olympiads themselves are separate competitions each with its own organising body, even though they are loosely grouped together as "ISOs". The aims of each ISO are to promote a career in science; to challenge the brightest students from around the world; and to compare the various teaching systems of each country.
Although the competitions are aimed for secondary school pupils, the standards of the exams are extremely high. In fact, in several countries, achieving a high ranking in any ISO guarantees access to a university of choice and a fellowship.