Community energy actors have emerged as significant players in European energy transitions. This dissertation uncovers the role of community energy actors as policy entrepreneurs. Despite being newcomers with limited resources, these actors successfully advocated for change within EU and German political landscapes. By empirically comparing and contrasting the EU's Clean Energy Package and Germany's renewable energy policy reforms between 2012 and 2019, this study explores how community energy actors and the concept of community energy have been institutionalized in different ways. This book contributes to a more nuanced understanding of the potential and limitations of political agency, discourse, and power in promoting sustainability transformations by examining the emergence of community energy actors and its connection to policy shifts.