The whole electrical system is facing a deep transformation with the purpose to integrate renewable energy sources (RES) and become more sustainable, a challenge that requires huge investments and the development of new mechanisms, mainly for the distribution sector and the electricity market. In this setting, demand-side flexibility (DSF) is stated to be a crucial tool to accommodate the grid changes and its management, optimizing renewable energy use and taking advantage of the arising active role of customers. Among the others, energy communities (EC) are playing their role in the European transition towards a less fossil fuel-dependent electricity system. Born under the Clean Energy Package to promote energy decentralization and people engagement, they are defined as voluntary organizations of people, autonomously ruled, which decide to be involved in distributed generation and related activities to provide economic, social and environmental benefits to their members rather than to be profit-driven.