'Inclusion' has emerged as a prominent theme in peacemaking. However, its exact meaning remains vague, as do assumptions about the relationship between inclusion and peace. This article seeks to problematize the research, policy and practice of inclusion. Focusing on United Nations (UN) peacemaking, we ask how the object of inclusion has been framed, and based on what strategies and underlying rationales. We do so against the backdrop of emerging debates about an agonistic peace, which suggest that violent antagonistic relationships can be overcome if peace processes enable contestation between adversaries. This requires that peacemakers recognize the constitutive role of difference in political settlements. We identify three distinct strategies for inclusion, with corresponding framings of the included. Firstly, inclusion can be used to build a more legitimate peace; secondly, to empower and protect specific actor groups; and thirdly, to transform the sociopolitical structures that underlie conflict. The first strategy frames the included in open terms that can accommodate a heterogeneity of actors, the second in closed terms pertaining to specific identity traits, and the third in relational terms emerging within a specific social, cultural and political context. In practice, this leads to tensions in the operationalization of inclusion, which are evidence of an inchoate attempt to politicize peace processes. In response, we argue for an approach to relational inclusion that recognizes the power relations from which difference emerges; neither brushing over difference, nor essentializing single identity traits, but rather remaining flexible in navigating a larger web of relationships that require transformation.