Thursday's G20 meeting in London is not going to change the world. But it can and must make a worthwhile contribution to restoring confidence in the global economy and so - over time - help people everywhere get back to work.
What will success look like?
First, the world's leaders will have to behave themselves - and they have a strong incentive to do so. Financial markets would react badly if the meeting ended in disarray, and G20 delegates would be held responsible. The chances of success here have been improved by a compromise between the two main camps: one led by the Americans, who want to concentrate on what they see as the immediate steps necessary to boost the world economy; and the other driven by France, Germany and the other big eurozone countries, who are more interested in longer-term reform of financial markets.
So Thursday's agenda will reflect two main streams of work, one dealing with short-term economic policy and the other with the structural changes necessary for sustainable growth.
There's no one-size-fits-all approach when it comes to a fiscal stimulus, and national leaders will be reluctant to make specific spending commitments. The best hope is probably for a clear framework showing how countries are going to share the stimulus burden and recapitalise their banking systems, along with a process to check countries are honouring their pledges.
On the structural changes, there have been clear signs of convergence in recent weeks between the ideas for financial reform being developed by regulators in the US, the eurozone and Britain. These will take time to get right: for example, legitimate trade could be damaged by rushed efforts to improve international tax transparency. The important thing is that big countries are engaging seriously with the problems, and moving broadly in the same direction.
As well as grand visions, Thursday's meeting must deliver tangible results - especially in the critical area of world trade. November's summit in Washington delivered airy promises about completing the Doha world trade deal and rejecting protectionism. Since then, the world has moved backwards, with the majority of G20 countries pushing up barriers, and world trade this year heading for its steepest decline in decades.
Commitments will have to be a lot crunchier this time round. Specific and substantial agreements are needed to improve the supply of trade finance. A detailed road map towards completion of Doha has to be drawn up; and much greater transparency about trade-distorting policies is required. The WTO and IMF should be empowered to name and shame those who break promises.
Finally, G20 leaders have large responsibilities to help economies in the developing world. This will require much easier access to increased IMF lending facilities, more effective engagement with the regional development banks, and a willingness to give emerging economies a much greater say in the way the IMF is governed. All this adds up to a big, complex package, which must be judged in the round rather than on the basis of a single component such as the size of the fiscal stimulus.
Will it all be worthwhile? Everyone knows events like this tend to produce bland promises and hot air. But a global economic crisis requires a global response. The very fact that Thursday's meeting is taking place at all has forced world leaders to address problems they might have preferred to ignore. The process needs to continue, with new milestones on the way. So another sign of success would be an agreement to hold a further G20 meeting this year.
For the sake of London's commuters, let's hope it is somewhere else.
Richard Lambert, CBI director-general news.cbi.org.uk.