The number of participating countries has grown steadily over the years. After the initial set of Eastern Bloc countries, many European countries joined since the 1970s, as well as Asian and American countries starting in the 1980s. Between 1990 and 2000 alone, the total number increased from 32 countries to 63. African countries have been joining since the 2000s. After accession into IPhO, every country must notify the others within five years about its willingness to host the IPhO. The venue of the Olympiad is decided for years ahead. With over 80 actively participating countries today, each IPhO is a big event with around 700 attendees and a total budget of several million euros. A small fraction of the cost is covered by a participation fee of around €3500 per team, which was introduced in 1997 on a voluntary basis and made obligatory in 2013.