Welcome!

Welcome to the 21st Conference on Complex Systems, CCS 2025! The CCS is the flagship annual meeting for the complex systems research community, operating within the framework of the Complex Systems Society. This special 21st anniversary conference is organized within the University of Siena (Siena, Italy), in the magnificent Unesco Heritage City of Siena. Previous editions took place in London/Exeter 2024, Salvador de Bahia 2023, Palma de Mallorca 2022,Lyon 2021, Online 2020, Singapore 2019, Thessaloniki 2018 and Cancun 2017.