This paper discusses the unique linkage of two international regimes – the World Trade Organization (WTO) and the Kimberley Process. Whereas the WTO is responsible for the reduction of existing barriers to trade, the Kimberley Process restricts the trade of diamonds originating from war-torn regions. These two regimes with their fundamentally different missions have been linked with the establishment of a WTO diamond waiver. A waiver is an exception clause agreed upon by the WTO Ministerial Conference and allows Member States to use trade measures otherwise forbidden under WTO rules. Based on regime theories, this paper analyses the role of the civil society, the governments and the diamond industry in linking the WTO with the Kimberley Process. The aim of the paper is to critically apply regime theories to a case of regime interaction. It highlights the advantages as well as the limits of regime theories and introduces the concept of constitutionalism as a new input for the study of regime interaction.