If the growing demand for global governance breathed new life into the established G7/8 and the more recent G20, it raised questions about the evolving and optimal relationship between them. One answer arose from the G20’s third summit, when it proclaimed the G20 would govern global finance and economics, while the old G8 would focus on development and security. Yet this rough division of labour did not address which issues lay within each category and how interconnections would be addressed to create comprehensive, coherent global governance for a complex world. This volume considers these questions. It explores the summits’ performance, the division of labour during their coexistence, their comparative strengths and limitations, and how the future partnership could be improved to benefit the global community. The authors explain the recent evolution and performance of the G8 and G20 summits and their evolving empirical relationship. They consider the G8/G20 relationship with other actors engaged in global governance, notably the major multilateral organizations and civil society. They assess G7/8 and G20 effectiveness and accountability. And they identify, based on this empirical and analytical foundation, how the relationship can be improved for today’s tightly wired world.