This open access book is a logical follow-up to European Guide to Power System Testing: The ERIGrid Holistic Approach for Evaluating Complex Smart Grid Configurations. Renewables are pivotal for reducing greenhouse gas emissions and combating global warming. However, their intermittent nature and limited storage capabilities present challenges for power system operators in maintaining power quality and ensuring the security of supply. Meanwhile, advancements in automation and communication technologies provide opportunities for developing intelligent solutions, transforming traditional power systems into Cyber-Physical Energy Systems (CPES). Despite progress, there is a growing need for integrated approaches to evaluate and validate these increasingly complex systems. The ERIGrid 2.0 project addressed this by focusing on the validation and testing of smart grids. The book includes validation scenarios, advanced simulation tools (e.g., co-simulation, real-time simulation, hardware-in-the-loop), and practical test cases. It highlights sector coupling and multi-energy systems as well as RI integration while addressing educational needs to support researchers, industry professionals, policymakers, infrastructure operators, and educators. By bridging smart grids and smart energy systems, ERIGrid 2.0 facilitates the deployment of innovative, sustainable energy solutions, accelerating the transition to resilient and integrated energy systems across Europe.