The world's eight richest countries have reached a landmark debt relief deal to alleviate global poverty.
The main beneficiaries of the deal could be Africa's poor
The move provides relief for poor, indebted nations, mostly in sub-Saharan Africa, freeing up much-needed revenue.
Announcing the deal at a meeting of G8 finance ministers in London, the UK's Gordon Brown said now was "not a time for timidity but a time for boldness".
The UK, which will host a summit of G8 leaders next month, has vowed to make poverty reduction a priority.
The plan, which was devised by the UK, secured the backing of the US administration on Friday - paving the way for its adoption at the London meeting.
Under the deal, the World Bank, the International Monetary Fund and the African Development Bank will immediately write off 100% of the money owed to them by 18 countries - a total of $40bn (£22bn; 33bn euros).
Between them, it will save those countries a total of $1.5bn a year in debt repayments.
UK Chancellor of the Exchequer Gordon Brown said up to 20 other countries could be eligible if they meet targets for good governance and tackling corruption.
The total package - which needs to be approved by the lending institutions - could be worth more than $55bn.
"We are presenting the most comprehensive statement that finance ministers have ever made on the issues of debt, development, health and poverty," Mr Brown said.
He added that the plan set the stage for July's G8 summit, where world leaders intend "to forge a new and better relationship, a new deal between the rich and poor countries of the world".
US Treasury Secretary John Snow hailed the agreement as "historic".
Relief groups welcomed the plan as a step in the right direction - but said some it should be extended to cover more developing countries.
"The debt deal is very good news for people in the 18 countries that will immediately benefit," said Romilly Greenhill of ActionAid.
DEBT RELIEF PLAN
Debts written off for 18 countries - total $40bn
Debt repayments saved by the group each year - $1.5bn
Nine more countries to qualify within 18 months - takes total to $55bn
UK's contribution over next 10 years: $700-$960m
US contribution: $1.3bn-$1.75bn
Africa's total external debt: $300bn
"But it will do little to immediately help millions in at least 40 other countries that also need 100% debt relief."
Earlier John Nagenda, an adviser to Ugandan President Yoweri Museveni, told the BBC it was time for rich nations to deliver on their promises.
"I should be more apologetic and say please help us but where I come from we believe that if you are better off than someone else you help them. It's as simple as that - it's a moral duty."
The G8 countries are the United States, Canada, Britain, France, Germany, Italy, Japan and Russia.
Thirty-eight countries are eligible for debt relief under the HIPC (highly-indebted poor countries initiative). The 18 that have reached completion point, and will therefore qualify for immediate debt relief, are shown in bold:
, Burkina Faso
, Burundi, Cameroon, Central African Republic, Chad, Comoros, Democratic Republic of Congo, Ethiopia
, Gambia, Ghana
, Guinea, Guinea Bissau, Guyana
,Ivory Coast, Liberia, Madagascar
, Malawi, Mali
, Mynamar Nicaragua
, Sao Tome, Senegal
, Sierra Leone, Somalia, Sudan, Togo, Tanzania
, and Zambia
Debt campaigners argue that an additional 24 countries should be included in any debt relief plan, including such large debtors as Nigeria, Bangladesh and Indonesia.