This chapter examines the role of international finance for post-war transitions and its relationship to international law. That relationship is considered in two respects: first, the international legal norms relevant to ‘who should pay?’; and second, the relevance of international aid to the development of international law. Section 2 tracks the evolution of post-conflict funding for settlement implementation and reconstruction in light of historical transformations in peace-making practice; and addresses the financial demands on conflict-affected states. Urgent needs for international aid to finance settlement implementation and peacebuilding, raises questions about whether third states might have a duty to provide finance. Thus, Section 3 evaluates prospects for international legal duties to provide that aid. The relevance of post-conflict finance and aid conditionality to the development of international law is considered in Section 4 to shed a different light on debates about an emerging law of peace-making or lex pacificatoria.