Climate change has become an important issue for the environmental movement and for other social movements, which are increasingly engaged in global climate activism. This chapter discusses comparative research literature on the environmental movement and green global governance, engaging in the debate on social movement institutionalization and globalization. It argues that the analysis of institutionalization, which in previous research mainly concerned national political contexts, needs to be re-conceptualized in light of developments that were conceptualized in terms of globalization and neoliberalism. To contribute to such re-conceptualization, the chapter introduces the concepts of de-politicization and responsibilization, arguing that a key dimension of current climate activism is a politics of responsibility. It provides some general methodological reflections, addressing both our study of the global public sphere of the Conference of the Parties (COPs) and the four national cases. Finally, the chapter presents an overview of the key concepts discussed in the subsequent chapters of this book.