This book CCIS 2486 constitutes the refereed proceedings of the 9th International Conference on Modelling and Development of Intelligent Systems, MDIS 2024, held in Sibiu, Romania, during October 17-19, 2024. The 16 full papers were carefully reviewed and selected from 42 submissions. The MDIS 2024 focuses on Machine Learning, Intelligent Systems for Decision supports, Modelling and optimization of Dynamic Systems, Evolutionary Computing and Metaheuristics, Security and Cryptography in Dynamic Systems.