Transnational private regulation (TPR) includes a large number of private regimes that regulate the behaviour of multinational firms and their interaction with investors, consumers, local communities. It consists of regulatory regimes designed and implemented by private actors, often in collaboration with international organisations. TPR standards are voluntary. TPR’s legitimacy is linked to and partly based on its effectiveness. Private and public regulation at transnational level are intertwined and international organizations play a significant function in making TPR effective. The chapter examines these regimes and tries identifying determinants of regulatory convergence and divergence. Convergence may concern procedural and/or substantive standards. Do private transnational regulatory models vary? Are they converging towards common characteristics? What are the factors determining divergences or convergences? The main question concerns the impact of international regulatory cooperation on divergence or convergence of transnational regulatory models. The paper demonstrates a correlation between forms and instruments of cooperation and modes of convergence. Firstly, the analysis shows that conventional comparative methodology used for state laws is unsuitable to compare transnational private regimes. Secondly the determinants of convergence or divergence of transnational regulatory models differ from those affecting the evolutionary patterns of State legal systems.