The transition to a sustainable energy future depends critically on the effective integration of renewable energy sources. However, their inherent variability introduces significant complexity into power grid operations. Coupled with evolving technologies, controllable loads, sector coupling, regulatory changes, and market liberalisation, today’s energy systems demand new operational paradigms. In-telligent automation and advanced control concepts are essential to transform traditional grids into smart, adaptive infrastructures. Over the past two decades, extensive research, innovation, and demonstration projects have laid the groundwork for smart grids and energy systems. More recently, the concept has expanded beyond electricity to encompass multidomain, cyber-physical energy systems, so-called smart energy systems. While these developments offer promising capabilities, they also highlight the growing need for robust system-level design, validation, and testing methodologies. Current tools and frameworks remain immature for the complexity of real-world deployment. This talk addresses these challenges by presenting key concepts, methods, and tools for the design and validation of cyber-physical energy systems. It also emphasises the critical role of human expertise, engineers, researchers, and pro-fessionals equipped to navigate the interdisciplinary demands of future energy systems.