Social movements, trade unions and political parties across the world are increasingly deploying the imaginary of "energy democracy" to advocate for renewable energy transitions that fundamentally reconfigure power relations, governance and decision-making within the sector. This thesis contributes to nascent debates around how energy democracy might be theorised and enacted, taking a specific focus on the democratisation of urban energy networks in two cities: London and Barcelona. The core argument of the thesis is that a distinction between two internally related conceptualisations of energy democracy is theoretically and politically generative. Thus, I explore the differentiated political possibilities opened and closed by an approach to energy democracy that foregrounds the transformation of institutions of energy governance, and an approach that seeks to broaden agency within the energy system. In making the argument, the thesis draws upon, develops and forges new connections between a range of scholarly debates and literatures, including those around energy geographies, post-politics, state theory, and social reproduction. In doing so, a scholar-activist perspective is pursued, with the thesis departing from ethnographic engagements with a range of struggles within which I am embedded as an activist participant to varying degrees, and documenting the myriad complications, frustrations, and causes for hope that ensue.