From extending energy access in the southern hemisphere to decarbonizing grids in the northern hemisphere, decentralized energy systems are becoming a feature of a global energy transformation. Alongside techno-economic forces, issues such as citizen engagement, environmental justice, social equity and acceptance are powerful forces shaping these transitions. This chapter focuses on public participation and user engagement in socio-technical transformations of urban energy infrastructures in order to better understand participatory methods and the roles of publics in transitions. Focusing on Smart Local Energy Systems (i.e., local projects that integrate renewable energy, electric vehicle infrastructure, battery storage and ‘smart’ energy monitoring) and sustainable heating, case studies describe how public engagement has been used to enable system-wide transformation. Social innovation and co-creation are introduced as methods which involve citizens in developing and implementing technological change to support the move away from fossil fuel dependence toward low carbon energy. Both methods acknowledge the tensions arising between instrumental approaches that are labeled as participatory, but which exhibit clear asymmetries of power, knowledge and resources, while demonstrating the potential of collaborative transitions.