This course introduces students to simulation and the rigorous analysis of operational systems in various contexts (production, services, logistics). It presents tools to evaluate system performance, identify bottlenecks, analyze flows, assess the impact of variability, and support capacity management decisions. Particular emphasis is placed on discrete-event simulation, used as an analytical tool to model complex systems, test scenarios, and inform decision-making. The course examines key levers for designing systems that are efficient, adaptable, and sustainable over time. It combines fundamental concepts, quantitative methods, and practical case studies to equip students with the skills needed to diagnose issues and design operational solutions tailored to dynamic and uncertain environments.