Leaders from 25 European states have signed a treaty to prevent the 17 European Union countries from running up huge debts.
They hope the treaty will help their countries overcome a two-year debt crisis. But there is still much work to be done.
"It will bring us, as it were, the economic and monetary union that is finally walking on two legs," said European Council President Herman Van Rompuy, who oversaw the drafting of the treaty.
Britain and the Czech Republic did not sign the treaty.
Meanwhile, other leaders must now get the agreement ratified at home.
"You now all have to convince your parliaments and voters that this treaty is an important step to bring the euro durably back into safe waters. I am most confident you will succeed," Van Rompuy told the heads of state and government.
"The treaty is short and sharp," he added. "Its benefits are clear. And above all, you are all gifted politicians; otherwise you would not be here."