International Junior Science Olympiad (IJSO) is a competition in science for students who are fifteen years or younger on 31st December of the competition year. IJSO aims to promote interest in science among school students, exposing them to problem solving, critical thinking and experimentation. Over the years IJSO aims to positively impact science and mathematics education at school level.

IJSO is held in December every year, in different countries. The academic competitions of the IJSO include challenging tests in topics of science, both as theory questions and practical tasks. The tests are designed to address students' understanding of concepts, and their ability to apply concepts to the situations described in the tests.

An important aim of the Olympiads is for young people to experience different cultures and to bring about interactions between students from across the world. The Olympiads thus have a potential to promote global peace and understanding.

The IJSO statutes state that no country may have its delegation excluded from participation on political grounds, lack of diplomatic relations, lack of recognition by the government of the organizing country, imposed embargoes, or other similar reasons. It is expected that the team representing the country has been selected after some form of national effort.

Participation in the IJSO either by a host country, a delegation or an observer, signifies acceptance of the statutes governing the IJSO.