This chapter examines the extent to which environmentalism has emerged as a viable ideology in its own right. It begins by charting the origins of the rise of the environment as an issue in relation to global and national political systems as well as the point at which it might be possible to identify the emergence of a distinct Green agenda. It then analyses the range of environmental thinking and the embedded critique, ideal, and programme that defines Green ideology, with particular emphasis on classical liberalism and neo-liberalism, Green conservatism, eco-socialism, social ecology, and eco-feminism. It also explores the impact that Green policies have had in shaping the policy agenda and concludes by looking at the main challenges that face the consolidation of Green thinking and action. To illustrate these various issues, the chapter presents case studies, one of which relates to global climate change.