This book constitutes the refereed proceedings of the 9th International Conference on Model and Data Engineering, MEDI 2019, held in Toulouse, France, in October 2019.The 11 full papers and 7 short papers presented in this book were carefully reviewed and selected from 41 submissions. The papers cover broad research areas on both theoretical, systems and practical aspects. Some papers include mining complex databases, concurrent systems, machine learning, swarm optimization, query processing, semantic web, graph databases, formal methods, model-driven engineering, blockchain, cyber physical systems, IoT applications, and smart systems.