International institutions are prevalent in world politics. More than a thousand multilateral treaties are in place just to protect the environment alone, and there are many more. And yet, it is also clear that these institutions do not operate in a void but are enmeshed in larger, highly complex webs of governance arrangements. This compelling book conceptualises these broader structures as the ‘architectures’ of global governance. Here, over 40 international relations scholars offer an authoritative synthesis of a decade of research on global governance architectures with an empirical focus on protecting the environment and vital earth systems. They investigate the structural intricacies of earth system governance and explain how global architectures enable or hinder individual institutions and their overall effectiveness. The book offers much-needed conceptual clarity about key building blocks and structures of complex governance architectures, charts detailed directions for new research, and provides analytical groundwork for policy reform. This is one of a series of publications associated with the Earth System Governance Project. For more publications, see www.cambridge.org/earth-system-governance.