After a decade-long large-scale violent conflict, the Pacific island of Bougainville in Papua New Guinea has gone through another decade of post-conflict peacebuilding and at present is confronted with the task of state formation. Peacebuilding has been a success story so far, and the prospects of state formation look promising. The maintenance of order, security and justice in post-conflict Bougainville is based on legal pluralism, with strong customary law and strong customary non-state policing. The violent conflict on Bougainville was a hybrid social-political exchange, with the causes and motivating factors stemming from both the sphere of statecentred politics (‘war of secession’) and the local societal realm in which non-state customary issues (land conflicts, pay back etc.) played a major role. This article explores the specific features of post-conflict peacebuilding on Bougainville that flow from this context, focussing on the local capacities, but also acknowledging the contribution of international peacekeeping, particularly through the United Nations and a regional Peace Monitoring Group. Based on the Bougainville experience, the article develops a critique of the conventional Western peacebuilding-asstatebuilding approach to fragile post-conflict situations, and it critiques the accompanying focus of external actors on capacity-building of state institutions for maintaining order and internal peace. It makes a case for an alternative approach which acknowledges the hybridity of political order and the co-existence and interplay of state and non-state providers of security and justice. Positive mutual accommodation of state and non-state customary institutions are presented as a more promising way to sustainable internal peace and order than the attempted imposition of the Western Weberian model of the state.