Over the last several years, the environmental regulatory system has undergone radical changes. Various private normative schemes, ranging from corporate codes to environmental management systems, environmental reporting standards, project-finance codes and green indexes, have assumed an increasingly important role in the regulatory arena. The emergence of private environmental governance as an important transnational phenomenon raises two interrelated puzzles: efficacy and legitimacy. Underlying the efficacy puzzle is a deep-seated suspicion toward "soft" legal instruments, which to some observers represent nothing but a coordinated form of "greenwash." The legitimacy question reflects a contrary concern — that these private regulatory structures represent new forms of global authority that are in need of distinctive legitimization. The Article begins with an outline of this new global terrain, exploring its historical evolution. It argues that the multiple links and cross-sensitivities between the different global private regimes have created a novel ensemble regulatory structure with positive enforcement and normative externalities. The Article then moves to examine the question of efficacy more generally, developing a nuanced understanding of the social dynamic of "soft-law" regulation, which rejects the binary logic underlying the "soft law"-"greenwash" narratives. Regarding the political dimension, the Article argues that this new ensemble network has brought about a new transnational political sphere which is associated with an extensive, cross-institutional quest for legitimacy. The Article then turns its focus to the field of sustainability indexes, focusing on the two leading global indexes: FTSE4Good Index Series and Dow Jones Sustainability Indexes (DJSI). These indexes are taken as a prototypical case of transnational private ordering. Drawing on a close analysis of the indexes’ guiding documents and on interviews with senior executives from both organizations, the Article considers the unique features of these indexes as forms of governance and the paths through which they claim to affect society. It then moves to explore the mechanisms of legitimacy employed by FTSE4Good and DJSI, highlighting their distinctive visions of legitimization. A close examination of sustainability indexes generates insights, I will argue, regarding the field of private global environmental governance as a whole. In particular, it highlights both the new political opportunities created by the evolving network of transnational governance and the limits this new structure sets for radical critique.