The congress takes place once a year, typically on the first weekend of September. Each year it is hosted in a different city. For example, the 2025 edition is held in Graz, Austria from September 4–7, 2025. (The 2024 edition was in Loutraki near Athens, Greece, and so on.)
Be sure to check the official site for the announcement of next year’s location and dates, as the host city changes annually. The event spans Thursday through Sunday of that weekend.
