Officially it's the United Nations Conference on Sustainable Development, but everyone is just calling it Rio+20. That is, twenty years after the 1992 Rio Earth Summit.
Over June 20-22, world leaders (or, in many cases national environmental heads) are getting together in Rio to "focus on two themes: (a) a green economy in the context of sustainable development poverty eradication; and (b) the institutional framework for sustainable development."
The big question is whether nations will commit to concrete steps that will actually change the course of the global economy so that humanity doesn't keep despoiling the planet, overconsuming natural resources, avert climate change, deploy non-polluting energy sources, all while attempting to reduce poverty and reduce income and energy inequality.
It's a tall task, no doubt about it, and time is running out before we cross critical tipping points where it will be too late to prevent ecological and civilizational catastrophe.