This book constitutes the refereed proceedings of the 9th Global Symposium on Smart Computing and Systems, G3S 2025, held in Beni Mellal, Morocco, during November 27–29, 2025.The 30 full papers included in this book were carefully reviewed and selected from 81 submissions. They were organized in topical sections as follows: Intelligent Models and Smart Decision Systems; Connected Intelligence and Distributed Architectures; and Secure, Trusted, and Data-Driven Ecosystems.