This open access book brings together research developed within national and European initiatives, offering a broad overview of selected technical, methodological, and policy-oriented developments relevant to next-generation energy systems. The contributions address different aspects of increasingly interconnected energy networks, including optimization and dynamic modelling of multi-vector infrastructures, cyber-physical validation and real-time simulation, as well as socio-economic and governance considerations. Together, they explore the opportunities and challenges associated with sector coupling, digitalization, and coordination across energy domains, highlighting the need for suitable tools for simulation, planning, and control, alongside appropriate regulatory, cybersecurity, and socially aware approaches. Organized into three thematic sections, the book covers: (i) methods for modelling, optimization, and control of multi-energy systems; (ii) enabling technologies, cyber-physical platforms, and experimental infrastructures supporting more digitalized and interconnected energy networks; and (iii) socio-economic, regulatory, and governance perspectives relevant to the transition toward more sustainable, inclusive, and resilient energy systems.