Private governance has proliferated in world politics, operating alongside formal regulatory systems by engaging in rule-making, promotion and implementation of norms, monitoring and verification, adjudication of compliance, and the imposition of sanctions. The rise of private forms of governance raises two basic questions for the study of global governance. First, what explains the emergence and proliferation of private governance? Second, what are the consequences of private governance on the effectiveness and legitimacy of global governance? Accordingly, after introducing private governance as an emerging concept in scholarly debates on transforming world politics as well as elaborating on different sets of actors engaged in private regulation, this chapter summarizes key insights into the emergence of private governance and its consequences for the effectiveness and legitimacy of global governance and concludes with the lessons learned and avenues for further research.