The US city of Pittsburgh is welcoming world leaders, amid calls for tougher action to prevent a new economic crash.
The G20 gathering of major powers comes almost six months after a landmark London summit when an historic deal was struck to tackle the global crisis.
In Pittsburgh, those in power will be judged on whether they have lived up to their earlier promises.
And with protesters expected in huge numbers,
a massive police presence is in place.
Ahead of her expected re-election on Sunday, Angela Merkel warned lessons from the economic downturn should be learned.
Before leaving Berlin, the German Chancellor expressed fears the G20 could be sidetracked by other economic themes.
“Pittsburgh will be decisive in determining whether the subject of financial market regulation continues to be a central issue,” said Merkel.
Whatever focus the forum takes, its outcome is unlikely to satisfy anti-globalisation activists who have been protesting outside the European Central Bank in Frankfurt.