This chapter considers the role of liberal leadership and informal institutions like the G20 in operation of the liberal international order (LIO). The LIO arose with and nurtured the rise of liberal economic and political forces that emerged in the West during the Cold War and then expanded globally. The institutional mechanisms created to advance prosperity and maintain stability were principally formal in nature: the Bretton Woods and United Nations institutions, the International Monetary Fund, the World Bank and the General Agreement on Tariffs and Trade that became the World Trade Organization. But these formal institutions have been accompanied by informal organizations such as the G20. But these formal and informal forms of global governance are now challenged by the emergence of Donald Trump, which has the potential to threaten the continued existence of the LIO. The G20 represents an important site of liberal leadership to sustain the LIO.