Climate change, strong dependence on non-renewable energy sources and alarming levels of global energy poverty: the current scenario highlights the profound need for an energy transition, emphasizing energy efficiency procedures and increasing the share of renewable energy sources in the global energy systems. However, this process should occur in a fair way, where the citizens should have an active voice in the decisions. Citizens will no longer be seen only as energy consumers, but increasingly, they will have the knowledge and foundation to be part of this transition, as well through distributed generation systems. In this context, local collective energy initiatives play a key role in increasing energy citizenship, primarily through Renewable Energy Communities. Albeit it is a very broad and diverse concept, the expansion of these communities entails various economic, social, and financial benefits for the locals, in addition to potentially reducing energy poverty and increasing energy justice. This dissertation aims to present a broad review of the concept of a Renewable Energy Community focused on the European and Portuguese context, and it interlinks with associated topics such as energy poverty, energy citizenship and distributed generation. In addition, it systematizes a set of study cases to uncover key activities, technologies, advantages and challenges and to explain how these organizations work to reduce energy poverty and increase citizen participation. In this context, a real-world study case is explored in detail through the Telheiras Renewable Energy Community development, where the implementation process was followed and is reported and key outputs include photovoltaic simulations carried out in six buildings of the community.