Governance for sustainability is one of the great current challenges for political decision-makers, in Europe and beyond. The vital question for European societies is to design effective, stable and legitimate governance systems at local, national and international levels that can ensure a co-evolution of nature and human societies under the overarching goal of sustainable development. This is the starting point of this Action on Transformation of Global Environmental Governance. The Action addresses the current transformation of global environmental governance that can be described as (i) increasing trans-nationalisation, that is, the growing relevance of public and private actors beyond national governments; (ii) increasing supra- and trans-governmentalisation, that is, growing relevance of transnational and supranational institutions; and (iii) increasing fragmentation, that is, increasing segmentation of the policy process through additional layers of decision-making and parallel regulatory systems. However, these transformations are not sufficiently understood. This Action is designed to address this situation as it focuses on the causes and consequences of the transformation of global environmental governance as well as on its effectiveness, legitimacy and robustness. This Action will also increase the ability of policy-makers, business representatives and civil society to understand and influence current environmental governance.