We live in an era of remarkable transformations in how governance is supplied at the global level, as traditional means of intergovernmental institutions are being joined by a growing diversity of transnational arrangements. Yet, at present, we still have only a superficial understanding of what causes actors to adhere to transnational rules, norms, and initiatives once they appear, and especially what role domestic political, economic and social variables play in their decision making. Focusing on climate change as an issue exemplifying the tendency for complex governance interplay, this special issue provides a comparative political economy perspective on the increasing but uneven uptake of transnational climate governance (TCG). This article articulates a conceptual framework for the analysis, highlighting the interplay between transnational and domestic politics and how such interactions shape the incentives, opportunities, andmodalities of participation in transnational initiatives. An original data set of participation in transnational governance initiatives is introduced to capture the significance of the phenomenon and to provide a common basis to systematically address, for the first time, questions about the cross-national patterns of involvement we find across different arenas and types of TCG, be they networks of sub- or nonstate actors, private rules, or hybrid arrangements.