Gordon Brown announced the deal on behalf of the G20
Leaders of the world's largest economies have reached an agreement to tackle the global financial crisis with measures worth $1 trillion (£681bn).
The deal came at a summit of G20 countries in London, called to discuss plans to beat the economic slump.
We look at the details of the plan and whether it will work.
What has been agreed by world leaders?
The G20 has agreed to increase the resources available to the International Monetary Fund, which helps countries that get into difficulties, by $750bn.
It is also contributing $250bn to help counteract the contraction of world trade and fight protectionism.
And it has agreed tough new measures to regulate financial institutions, including sanctions against tax havens that do not disclose information.
Is there real substance in the deal or is it just hype?
There is some new real money in the deal, but not as much as the headline figure.
Much of the $250bn in trade finance will come from existing programmes of export guarantees in rich countries, with only $50bn for poor countries.
The proposal for $250bn in free money from the IMF is a dramatic new development - but only $19bn will be made available to the poorest countries.
The reform of the financial system will be important, but only for the next crisis.
Will it revive the world economy?
On its own, the deal will only have a limited effect on the world economic downturn which is still gathering pace. Only some of the money given to the IMF will be lent out, and it will have to be repaid with interest.
More important will be how far countries continue boosting their economies with fiscal stimulus. Gordon Brown said that would amount to $5 trillion by next year.
And fixing the broken banking system, especially in the US, still hangs in the balance.
What was left out?
There was little discussion of the misalignments among world currencies, with a falling dollar and pound, which are worrying some countries.
The Chinese proposal for a new international currency has been put on the back burner and will be discussed at a later date.
The idea of global imbalances - ie the need for China to spend more and the US to save more, which some believe was the origin of the crisis - was also not mentioned.