Contributor(s): Professor Jeffrey D Sachs | The G20 Summit is the world's key venue for addressing the current global crisis. Yet there are profound questions facing the Summiteers. What are the underlying causes of the global crisis? What are the priorities to speed economic recovery? How should the G172 (the 172 UN members not members of the G20) be represented? What are the most powerful tools for protecting the world's most vulnerable people, arresting financial contagion, restoring global demand, and creating a path to sustainable development? Does the world require a fundamental re-shaping of global institutions and modes of cooperation?