Energy system operation is the academic field and methodological approach concerned with the real-time planning, coordination, control, and management of complex energy infrastructures. It investigates the dynamic interactions between system components—including generation, transmission, distribution, storage, and consumption—to ensure reliability, economic efficiency, security, and sustainability under varying conditions and constraints. This concept is characterized by the need to handle uncertainty in supply and demand, manage technical limitations, integrate diverse energy sources, and optimize system performance across multiple objectives, making it critical for stable energy delivery and facilitating the energy transition.