The International Junior Science Olympiad (IJSO) is an annual in-person competition in the natural sciences — physics, chemistry, and biology — for students under the age of 16. It brings together national teams of young scientists from countries around the world to solve theoretical and experimental problems, with the goal of promoting scientific excellence and fostering international friendships among junior students.
The competition rotates host countries each year. The 2026 edition is held in Sofia, Bulgaria. Each participating country sends a team selected through its own national junior science competition. Students cannot apply individually; they must qualify through their country's national selection process.
The event is non-commercial and free for participants (travel and accommodation are typically arranged by national delegations). Visit ijsoweb.org for the current year's host, schedule, and links to national organizing committees.