Over the past twenty years, global efforts to combat climate change have become an increasingly complex matter. The central forum for multilateral, state-led climate governance, the United Nations Framework Convention on Climate Change (UNFCCC), has been complemented by numerous cross-border initiatives comprising both state and non-state actors, including non-governmental organizations (NGOs), firms, academia, cities, sub-national regions and international organizations. 2The broader institutional structure has developed from a single regime to a regime complex, 3 showing increasing signs of fragmentation and functional overlaps that threaten coherence and overall effectiveness. 4 In Ostrom’s words, global climate governance is best described as a polycentric system with ‘multiple governing authorities at different scales rather than a monocentric unit’. 5 However, while fragmentation is largely accepted in theory as a ubiquitous phenomenon in global climate governance, few empirical studies exist that map institutional complexity and consequently attempt to measure degrees of fragmentation or coherence. 6sures of institutional coherence or fragmentation in global climate governance. First, we present a mapping of all governance institutions that constitute the climate change regime complex, departing from Abbott and Snidal, Abbott and Keohane and Victor. 7 We include both international and non-state public institutions (for example, the UNFCCC and transnational municipal networks) as well as the broad range of bottom-up initiatives constituted by various mixes of actors, including firms, civil society, governments and international organizations. Second, we add the organizational, agent-based dimension of climate governance by showing how the institutional meta-structure is constituted by actors and their connections. To this end we have collected data on membership in all climate governance institutions that make up the regime complex, in total more than 10,000 unique organizations. As a third analytical step, we report on advances in measuring discursive structures in the climate change regime complex. Here we analyse how the 80 climate governance institutions relate to 4 pre-identified metadiscourses in environmental policy via their mission statements. In the discussion section we revisit the three complementary assessments of the current climate change regime complex to establish whether the overall institutional structure is fragmented, that is, polycentric, or rather centralized, that is, integrated. In the conclusions we reflect on how to advance this research agenda further.