One assumption underlying the work on industrial symbiosis (IS) is that certain social conditions must be fulfilled in order for firms to develop symbiotic linkages. In this article we add depth to this insight by using institutional capacity as an underlying concept for these conditions, and we propose that such capacity influences IS by altering the opportunity set of actors. We then test the assumption on a dataset of 233 projects aiming to develop eco-industrial parks. We find that the link between institutional capacity and the opportunities for symbiotic linkages perceived by actors is not always present and is more complicated than has been recognized thus far. We discuss potential alternative ways in which institutional capacity might influence IS and present ideas for future research to shed light on this important relationship.