Abstract. In climate change, as in other areas, recent years have produced a 'Cambrian explosion' of transnational institutions, standards, fi nancing arrangements, and programs. As a result, climate governance has become complex, fragmented, and decentralized, operating without central coordination. Most studies of climate governance focus on inter state institutions. In contrast, I map a diff erent realm of climate change governance: the diverse array of transnational schemes. I analyze this emerging system in terms of two theoretical frameworks developed to describe, explain, and evaluate complex governance arrangementsregime complex theory and polycentric governance theory-revealing fruitful avenues for positive and normative research. I conclude by arguing that the benefi ts of institutional complexity could be increased, and the costs reduced, through nonhierarchical 'orchestration' of climate change governance, in which international organizations or other appropriate authorities support and steer transnational schemes that further global public interests.