The political and territorial challenges facing Israeli and Palestinian peace negotiators are formidable and familiar. The economic obstacles to the creation of a viable Palestinian state are also formidable, but easier to make a dent in — if all the donors who claim to care about the Palestinians and peace live up to their promises.

On paper, this week’s international pledging conference was a huge success. Led by the United States, the European Union and Saudi Arabia, donors committed to contribute $7.4 billion over the next three years. That is almost $2 billion more than the Palestinian Authority had sought, though probably less than it really needs.

The conference owes at least some of its success to Tony Blair, who is coordinating international efforts to support Palestinian development. It was also helped by the Bush administration’s overdue attention to peacemaking since the Annapolis conference and by the serious economic recovery plan presented by the Palestinian prime minister, Salam Fayyad, an economist.

Life has been growing steadily grimmer in the West Bank and the Gaza Strip since the outbreak of the second intifada in 2000 and Israel’s crushing military counterattacks and economic blockades. Things got even tougher after the West suspended most of its support following Hamas’s 2006 election victory. Those aid spigots have now been reopened, at least to the West Bank where Palestinian Authority moderates, under President Mahmoud Abbas, are in charge. It is crucial that the people of Gaza also receive support. But that support should not flow through Gaza’s Hamas government.

Much of the money pledged on Monday will be needed just to keep Mr. Abbas’s government solvent. What the Palestinian economy really needs is private investment to reanimate commerce and revive trade with the world. That can only happen once Israel agrees to remove the barricades that seal off West Bank communities from each other and feels secure enough to ease the passage of goods through border crossing points.

To make a real difference, the billions pledged in Paris will need to be matched by diplomatic progress.