In chapter 8, I explore how a solidarist logic of cooperation has pushed states to expand the scope for global environmental action via international institution-building and international law. I am interested in understanding the extent to which this emerging system of global environmental governance has brought about a gradual greening of the sovereignty norm – a key marker of environmental solidarisation. This raises several key questions: To what extent has the consolidation of GIS’s commitment to environmental stewardship gone hand in hand with a strengthening of the solidarist agenda in international relations? Has the rise of global environmentalism served to redefine the meaning of sovereignty in an age of global ecological interdependencies? It promoted a deeper sense of common values and interests that transcend national boundaries, thereby helping GIS to evolve from a ‘thin’ to a ‘thick’ sense of community and common purpose?