This chapter examines the constructivist approach with respect to analyzing the G20. It begins with a broad overview of developments in constructivism since the 1990s, then indicates how recent constructivist scholars have built on earlier studies. The subsequent discussion focuses on the author’s research, which integrates constructivist insights with conceptual tools from other approaches, in analyzing global economic governance and the G20. It emphasizes how actors’ strategic, political, and cognitive authority influences the G20, as well as assessing constructivist understandings of the significance of organizational and policy norms, practices, and socialization. This includes an analysis of the construction of new policy norms and practices since the global financial crisis of 2008–09, for example in the contexts of macroprudential financial regulation and sustainable development. The chapter concludes that constructivist IR provides useful insights for enhancing the legitimacy of the G20.