Transition to a sustainable future requires not only technical but also societal changes, including changes in behavioral patterns and consumer roles. Renewable energy communities embody such changes: they are mainly residential communities that break with their passive consumer role and produce energy from renewable sources in order to meet primarily local needs. Although the number of these communities has increased remarkably in the last decade in many Western countries, as has the academic attention paid to them, we still have limited knowledge on how they are formed and operate. It is unclear how they get their members to work collectively on a voluntary basis for a common goal; that is, energy production at the local level, and overcome the challenge of free-riding. This article seeks to contribute to a better understanding of the institutional and social context in which these communities operate, as well as of the way they are created and function. Therefore, the research question addressed is: What factors influence renewable energy communities’ formation and organization? In particular, the interest is in strategies for group formation, task distribution, collective action, communication, decision making, and problem-solving. This paper addresses the research question through a comparative assessment of case studies in Germany and the Netherlands. It analyzes different communities—of distinct sizes, location, and using various technologies—and assesses the commonalities between them and their general practices that led to the successful project implementation. The results show that, contrary to Olson’s expectation about voluntary collective action, renewable energy communities can realize their goals based on the work of only a few volunteers who develop the project without receiving any additional reward and who also accept free-riding. However, the larger the community’s size and the complexity of the project, the more likely it is that they need to formally organize the procedure or count on external support.