This chapter explores the ideas and debates which shape global environmental politics. At least three types of socially constructed ideas play a key role in international environmental governance: world views, causal beliefs, and social norms. However, ideas are not universally shared, which means that ideological clashes are a feature of global environmental governance. The chapter looks at five of the major ideological debates that have marked the evolution of global environmental governance. The first two debates present conflicting world views: the first concerns the scope of environmental values, while the second examines the intrinsic values of non-human organisms. The following two debates concern causal beliefs: one is about the relationship between human intervention and environmental protection, while the other concerns the relationship between economic growth and environmental degradation. The last debate considers different social norms related to environmental justice and the appropriate behaviours expected towards historically marginalized populations.