Over the years, the International Congresses have grown dramatically, from just 22 participants in London (1946) to nearly 4,000 participants from 117 countries in Paris (2025)

• 23rd – Paris, 2025 — 3,835 participants from 117 countries
• 22nd – Tokyo, 2022 — 3,345 participants
• 21st – Buenos Aires, 2017 — 3,038 participants
• 20th – Granada, 2013 — 3,896 participants
• 19th – Bangkok, 2009 — 4,070 participants from 106 countries
• 18th – Durban, 2005 — 2,100 participants from 92 countries
• 17th – Vienna, 2001 — 3,550 participants from 113 countries
• 16th – Montreal, 1997 — 3,250 participants from 92 countries
• 15th – Adelaide, 1993 — 2,600 participants from 91 countries
• 14th – Seoul, 1989 — 3,500 participants from 104 countries
• 13th – Brighton, 1985 — 2,300 participants from 92 countries
• 12th – San Diego, 1981 — 2,500 participants from 83 countries, 1,011 papers
• 11th – Rio de Janeiro, 1978 — 3,500 participants from 92 countries, 1,200 papers
• 10th – Kyoto, 1975 — 2,300 participants from 55 countries, 900 papers
• 9th – Mexico City, 1972 — 2,000 participants from 66 countries, 834 papers
• 8th – Prague, 1969 — 1,800 participants from 62 countries, 896 papers
• 7th – Hamburg, 1966 — 2,100 participants from 81 countries, 800 papers
• 6th – Edinburgh, 1963 — 1,500 participants from 63 countries, 225 papers
• 5th – Washington, 1960 — 2,000 participants from 65 countries, 413 papers
• 4th – Paris, 1957 — 1,000 participants from 22 countries, 367 papers
• 3rd – Amsterdam, 1954 — 360 participants from 32 countries
• 2nd – Basle, 1952 — 150 participants from 18 countries
• 1st – London, 1946 — 22 participants from 17 countries