Formal transparency policies are increasingly prevalent in global governance institutions, partially attenuating the influence in these institutions of practices of secrecy inherited from interstate diplomacy. This article assesses the incidence and specific characteristics of formal transparency policies across a select group of institutions and outlines some of the justifications given for these policies-including justifications based on the publicness of these institutions-and for the more controversial exceptions to transparency, such as the exception for deliberative materials. It examines three drivers affecting the adoption, form, and content of transparency policies and other transparency measures in these institutions: spillover from national transparency laws and policies, growth in the reach and significance of authority exercised in and through global institutions, and criticism of global institutions by influential states and nongovernmental organizations. Twelve hypotheses are proposed about the effects, for states, nonstate actors, and global governance institutions, of transparency measures-formal policies and other steps to increase transparency-in global governance institutions. Finally, the article considers some implications of transparency measures for structures of political power and authority beyond the state and for global administrative law.