This 2-volume set of proceedings contains 62 selected full papers presented at the Fifth International Conference on Modeling, Computation and Optimization in Information Systems and Management Science (MCO 2025), held on June 4-6, 2025, in Metz, France, celebrating the 40th anniversary of DC (Difference of Convex functions) programming and DCA (DC Algorithms)-pioneering and highly influential methodologies founded by Pham Dinh Tao and Le Thi Hoai An. This first volume (Part I) features 31 articles exploring foundational and cutting-edge topics in optimization and decision science, which lie at the heart of Artificial Intelligence. It presents advances in DC programming and DCA, innovations in combinatorial optimization and its applications, emerging trends in decision models, and other pivotal topics shaping the field. These proceedings are intended to serve as a lasting reference and a source of inspiration for research and applications at the forefront of optimization, AI, and decision sciences.