Policymakers increasingly emphasize knowledge collaboration between academia and society as important means to generate innovations and solve complex issues. However, while recent literature on such collaboration suggests that knowledge needs to be integrated and generated across disciplines and sectors, there are surprisingly few studies that define what is meant by ‘knowledge’ or focus on the process of generating knowledge. Subsequently, the aim of this paper is to unbox ‘knowledge’ in knowledge collaboration by focusing specifically on how knowledge is understood by heterogenous actors during the process of generating knowledge. We build on insights from an in-depth case study and contribute to the literature on knowledge collaboration by bringing in theory on boundary work that specifically addresses the knowledge generation process. We argue that to better meet the expectations of collaboration, there is a need for more discussions and focus on the participating stakeholders’ heterogenous epistemological as well as ontological understanding.