The first part of Chapter 3 introduces the diverse roots of environmental thinking and identifies the normative core around which modern environmentalism is built. It traces the evolution of different strands of environmentalism and outlines the main debates that have shaped the evolution of environmental thinking and activism since the nineteenth century. The second part of this chapter identifies the different ways in which environmental ideas can be applied to the international realm. Employing the English School’s conceptual dyads of pluralism/solidarism and international/world society, it identifies four ideal types of how a green global order can be created: ‘Green Westphalia’ and ‘global environmental governance’, representing the pluralist and solidarist variants of a green international society; and ‘eco-localism’ and ‘eco-globalism’ as the pluralist and solidarist versions of a green world society.