The energy and building sector are vital to Europe’s environment and energy policies. In the current energy transition, the building sector is recognized as a cornerstone due to the possibility to easily adopt advanced control strategies and smart management systems. Thereby cost-effectively increasing buildings’ energy efficiency and flexibility, while improving building users’ comfort, productivity, and health. This cost-effective energy use reduction will render faster implementation of on-site and nearby renewable energy sources, facilitate demand electrification, hence reducing Europe’s energy dependencies. Achieving the building sector energy transition demands an improvement of the interoperability of European buildings with energy carriers and non-energy services. Buildings must play an active role in ensuring the reliability, resilience, and sustainability of the energy system, particularly in the face of evolving challenges such as climate change, resource constraints, and other threats (e.g., cybersecurity, geopolitical, etc.). Therefore, the aim of ENTRANCE is to enable smart-grid-ready and decarbonized buildings through the integration of energy efficiency, flexibility, on-site renewables, mobility, empowerment of end-users, and interoperability between buildings and district heating and electricity grids. The ambition of ENTRANCE is to develop and demonstrate solutions that promote building integration and active participation in the energy system and market through guaranteeing end-users’ comfort and empowerment while creating value for the economic actors of the energy landscape. Through four core principles based on integrated technology, digitalization, user engagement, and performance-driven economics, ENTRANCE solutions will be demonstrated in relevant environments. To generalize the solutions for different geographical regions, ENTRANCE includes demonstration sites from six different countries around Europe.