From a regional initiative in 1968 to a truly global competition uniting 80+ countries through demanding theoretical and experimental exams.
The first IChO ran in Prague (18–21 June 1968) with three countries — Czechoslovakia, Poland, and Hungary — and was theoretical only. In 1969 (Poland), the experimental exam was introduced and Bulgaria joined, with the USSR and GDR observing. In 1970 (Hungary), Romania, the USSR, and the GDR officially took part, and teams were capped at four students — a limit that continues today.
There was no IChO in 1971, but the event resumed in 1972 (Soviet Union), followed by 1973 (Bulgaria) and 1974 (Romania), setting the practice of choosing hosts years ahead. A milestone came in 1980: the 12th IChO in Linz, Austria — the first outside the Eastern Bloc — bringing broader participation. By1984 (Frankfurt, Germany), 21 countries were competing.
After the fall of the Iron Curtain, participation expanded rapidly across Asia, the Middle East, and the Americas. Today the IChO welcomes 80+ countries. Delegations bring up to four students and two mentors. Contestants face two rigorous five-hour examinations — one theoretical and one experimental.
The IChO flag was introduced in 1985 at the 17th IChO (Bratislava). It bears five colored flames symbolizing the burning colors of ionic compounds and the unity of the IChO community.