Energy controversies have been widely studied. Such studies are, however, generally based on either single case studies, providing rich and in-depth understanding of (local) dynamics of planning and implementation processes, or they focus on understanding responses to a specific technology (not bound to a location). Therefore these studies tend to overlook a key dynamic in controversy, namely that publics respond to projects by drawing on earlier experiences with a similar technology elsewhere, or with earlier experiences with other technologies in their vicinity. We refer to this dynamic as controversy spillover. The notion of controversy spillover helps to understand how the discursive space of controversy changes over time. In case studies, other controversies are usually considered as context, i.e. as an external condition. However, in order to understand the temporal dynamics of public engagement with energy projects, spillover from other controversies deserves to be investigated more as an object of interest, rather than as an external condition. The aim of this paper is to conceptualize controversy spillover as an important dynamic in controversies and to develop a research agenda. We identify three different types of spillover: 1) geographical (i.e. between the same energy technology in different locations), 2) historical (i.e. with respect to earlier experiences at the same location), 3) technology (i.e. between different technologies). Three empirical examples serve to illustrate the three types of spillover. We finalize the paper with a research agenda for further conceptualization and empirical analysis of the notion of controversy spillover.