This special issue explores norm diffusion, contestation and localisation in the contexts of political transition in general and post-war peacebuilding specifically. It engages with critical moments in which international diffusion endeavours meet local politics of norm contestation in societies undergoing post-war and/or post-authoritarian transitions. The 'third wave' of norm research offers an agency-based approach to the negotiation and contestation of the meaning of norms that is consistent with work in peacebuilding studies on the meeting between international norms and local realities in post-war contexts. By honing in on the 'normative powers' of local agents, their perspectives and capacities, and how these contribute to norm construction, the special issue provides theoretical and conceptual advances to capture these transition processes in the context of the Western Balkans.