This report presents Deliverables 2.1 and 2.2 of the Horizon 2020 SCCALE 203050 project (Sustainable Collective Citizen Action for a Local Europe). The aim of this project is to scale the growth of energy communities - or “Renewable Energy Communities'' according to the EU Renewable Energy Directive (RED II) - across Europe in the areas of energy efficiency, renewable energy production, district heating in households and non-residential buildings. This report is the first deliverable of Work package 2 (Research and Academic Validation) which seeks to gain a better understanding of how collective citizen actions in sustainable energy develop, grow, mature - in other words, how they come of age. This will be done by analysing, monitoring and evaluating experiences of collective citizen action and community engagement in the domains of sustainable energy (i.e. renewable energy, energy efficiency, and energy conservation). This report first presents the results of a literature review (i.e. Deliverable 2.1) – using both academic and grey literature - on energy communities and collective citizen actions contributing to sustainable energy transitions. However, the report goes beyond a literature study. Instead, it was developed as a collaborative effort between the research team at Delft University of Technology and community energy experts and practitioners using multiple interactive and feedback meetings. The central aim of this report is to generate insights into the actions and activities energy communities and citizen collectives undertake to develop and mature their organisations with the objective to scale, achieve transformative change, and make both a social and environmental impact. The report maps state of the art insights into collective citizen actions at the neighbourhood level, targeting energy efficiency and renewable energy technology measures alike. Moreover, it addresses relevant theory and good practice on actions and activities that energy communities can pursue, partly based on theory and partly based on case studies. In addition, the report also takes into account issues like energy poverty, energy democracy, energy justice, social inclusiveness, citizen engagement, multi-stakeholder management in neighbourhoods, the use of digital tools, and data protection (to cope with increasing cybersecurity issues). In addition, the report presents the development and design of a monitoring tool (Deliverable 2.2). The Development Progress Tool uses knowledge from the literature study. This is firstly used to elaborate the energy community maturity scale and framework as developed under the Horizon 2020 COMPILE project (Seebauer et al., 2022). The elaborated maturity index forms the conceptual basis and framework to develop a monitoring tool. The latter will be implemented, tested and validated among the five demonstration pilots of SCCALE 203050 in 2022-2023. @en