Process integration is the systematic combination and optimization of interconnected physical and chemical transformations within a complex system, focusing on the efficient management of energy, material, and information flows between constituent process units. As a methodological approach and research field, it investigates the principles governing the interactions and synergies among process steps. Key characteristics include employing a holistic system perspective to identify opportunities for resource conservation, waste reduction, and performance enhancement, such as maximizing energy conversion efficiency in power generation systems like nuclear reactors. Its significance lies in facilitating the design and operation of sustainable and highly efficient industrial and energy systems.