The current EU ‘Clean Energy Package’ aims to place local consumers at the heart of the energy transition. In the context of local energy systems with a weak or non-existing grid connection this implies to give the power of operating a renewable-based energy infrastructure to the local people, energy consumers and producers. Private people and organizations should be involved to establish energy island communities, which are based on self-management and -operation. Simultaneously, those communities will improve social cohesion and technical optimization of all energy vectors existing in the specific energy island. The goal of RENergetic is to integrate and demonstrate solutions that will foster a substantial increase of 1) energy efficiency and 2) the level of renewable energies and energy autarky by integrating three main energy vectors (electricity, heat, waste) in three heterogeneous urban energy islands, with an early involvement of the communities and a long-term economic viability: The New Docks in Ghent, Belgium (energy-aware housing), the Warta Campus in Poznan, Poland (data center heat for a campus) and the Hospital and Research campus in Segrate-Milan, Italy (demand response, including electric vehicles). This transdisciplinary endeavor is supported by innovative activities in all relevant areas. On the technical level, optimization and demand response approaches for cross-sector scenarios are combined in a hierarchical approach. This concept integrates innovative smart control strategies and machine learning based-forecasting methods. A thorough regulation analysis feeds into the creation of novel business models, market strategies and value networks on the economic and legal level. This ensures seamless integration with existing energy management systems and cooperation with external networks. Finally, an iterative approach of empowering the energy island communities with participatory structures will be applied on the social level.