Peacebuilding scholarship is one of several domains in the discipline of International Relations (IR) that has recently begun to pay closer and systematic attention to knowledge—its productions, constitutions, circulations, contestations, and effects. This chapter begins by giving an overview of the burgeoning literature on peacebuilding epistemics. In doing so, it identifies an ‘epistemic contraction effect’ that confines the analysis. Scholars focus not only on certain peacebuilding actors and on the ways in which they produce and use their knowledge, but also only on actors who are seemingly directly engaged in peacebuilding. One reason behind this state of affairs in the literature on peacebuilding epistemics, the chapter further argues, is underlying and unquestioned substantialist assumptions. As an alternative, the chapter proposes a shift to a relational approach that forms around the notion of an ‘interventionary object’. After detailing what this approach entails, the chapter illustrates the distinctiveness of such an approach in an analysis of the becoming of economic informality as an interventionary object, which has shaped peacebuilding ‘anti-informality’ projects in Bosnia and Kosovo