World leaders will gather in Pittsburgh on Thursday and Friday for the latest G20 summit.
The event costs tens of millions of dollars to stage and attracts the attention of campaigners and the world's media. This guide looks at what to expect.
What is the G20?
It is costing Pittsburgh an estimated $20m to stage the event
The Group of Twenty, to give it its full title, was originally set up after the Asian financial crisis in 1999 as a forum for finance ministers and central bankers to get their heads together.
The first top-tier G20 summit involving heads of government was held in Washington last year to discuss an international response to what was developing into the worst recession in 60 years.
Officially, its 20 members are: Argentina, Australia, Brazil, Canada, China, France, Germany, India, Indonesia, Italy, Japan, Mexico, Russia, Saudi Arabia, South Africa, South Korea, Turkey, United Kingdom and the United States of America.
But they are also regularly joined by Spain and the Netherlands as well as representatives from international institutions including the World Bank, the International Monetary Fund and the World Trade Organisation.
What does it do?
As financial crises tend not to respect international borders, the meetings are a way for leaders to come together to discuss - and hopefully agree - coordinated responses to financial problems whose effects ripple across the globe.
Security will be tight around the summit
At the time of the last major G20 leaders' summit in April, some feared the world was facing a 1930s-style depression, so the focus was on bringing about economic recovery... and quick.
Together, they said they would spend $5 trillion on measures to stimulate their economies and came up with funding pledges worth more than $1tn to help struggling nations.
But the G20 also turned its attention to what could be done to prevent a similar crisis happening in future.
Did they do what they said they would?
G20 PITTSBURGH SUMMIT
Leaders of the world's biggest economies will gather in Pittsburgh on Thursday and Friday for the latest G20 meeting in the wake of the global financial crisis
For full coverage of the G20 and the global recession go to our
It's a mixed picture.
By and large the financial pledges seem to be on track. Much of the money pledged to the International Monetary Fund for them to distribute - which makes up a large chunk of the $1tn - has found its way there. Though in one or two cases, accurate figures are hard to come by.
Not surprisingly, there is still a lot of work to be done on the thornier and more complex issues of reforming how the global economy is run, and regulating bankers and hedge funds.
BBC News online has put together a
so you can assess the G20's progress against a number of key promises.
So what should we expect from this summit?
Many of the major economies are beginning to climb out of recession or are expected to do so very soon - and that's due in part to
government stimulus packages.
So there isn't the same need for big spending commitments, but they will talk about the need to follow through with the ones already made.
Attention will be focused on reform and regulation.
Cracking down on bankers' bonuses
has popular appeal, so an agreement should be reached on that.
Less catchy is "regulatory harmonisation" - making sure countries sing from the same hymn sheet and don't try to attract companies with looser rules. That is on the agenda, too.
Discussions will continue over
whether China and India should be better represented
on the board of the International Monetary Fund.
And ideas about "rebalancing" the world economy, which have been floated by the US, will be debated. That's big stuff, changing the relationship between developed and developing economies that the world economy is built on.
On a much more practical level, the leaders will be mindful of the fact that although recovery may be starting, there are still very large numbers of people unemployed. Expect this to feature prominently.
And so, why Pittsburgh?
First of all convenience. Many of the leaders will have been in New York for the United Nations General Assembly, so it is is just a short hop to Pennsylvania for them.
Secondly, Pittsburgh ticks a number of presidential boxes.
Pittsburgh, the grimy old steel town that was once a powerhouse of American heavy industry has transformed itself - after the industry's decline - into a clean, green example of regeneration.
It tells a positive story about Obama's America
our correspondent Kevin Connolly says.
Just the sort of financial recovery a President would want to show off to visitors.