This is a defining moment for the world economy.

We are living through the first financial crisis of this new global age. And the decisions we make will affect us over not just the next few weeks but for years to come.

The global problems we face require global solutions. At the end of World War II, American and European visionaries built a new international economic order and formed the International Monetary Fund, the World Bank and a world trade body. They acted because they knew that peace and prosperity were indivisible. They knew that for prosperity to be sustained, it had to be shared. Such was the impact of what they did for their day and age that Secretary of State Dean Acheson spoke of being "present at the creation."

Today, the same sort of visionary internationalism is needed to resolve the crises and challenges of a different age. And the greatest of global challenges demands of us the boldest of global cooperation.

The old postwar international financial institutions are out of date. They have to be rebuilt for a wholly new era in which there is global, not national, competition and open, not closed, economies. International flows of capital are so big they can overwhelm individual governments. And trust, the most precious asset of all, has been eroded.

When President Bush met with the Group of Seven finance ministers last weekend, they agreed that we all had to deal with not only the issue of liquidity in the banking system but also the capitalization and funding of banks. It was clear that national action alone would not have been sufficient. We knew we had to send a clear and unambiguous message to the markets that governments across the world were prepared to act in a coordinated manner and do whatever was necessary to stabilize the system and address the fundamental problems.

Confidence about the future is vital to building confidence for today. We must deal with more than the symptoms of the current crisis. We have to tackle the root causes. So the next stage is to rebuild our fractured international financial system.

Last week, European leaders came together to propose the guiding principles that we believe should underpin this new Bretton Woods: transparency, sound banking, responsibility, integrity and global governance. We agreed that urgent decisions implementing these principles should be made to root out the irresponsible and often undisclosed lending at the heart of our problems. To do this, we need cross-border supervision of financial institutions; shared global standards for accounting and regulation; a more responsible approach to executive remuneration that rewards hard work, effort and enterprise but not irresponsible risk-taking; and the renewal of our international institutions to make them effective early-warning systems for the world economy.

Yesterday, French President Nicolas Sarkozy and European Commission President Jose Manuel Barroso were to meet with President Bush to discuss the urgent reforms of the international financial system that are crucial both to preventing another crisis and to restoring confidence, which is necessary to get banks back to their essential purpose — maintaining the flow of money to individuals and businesses. The reforms I have outlined are vital to ensuring that globalization works not just for some but for all hard-pressed families and businesses in all our communities.

It is important, too, that in the international leaders' meeting that has been proposed we seek a world trade agreement and reject the beggar-thy-neighbor protectionism that has been a feature of past crises.

There are no Britain-only or Europe-only or America-only solutions to today's problems. We are all in this together, and we can only resolve this crisis together. Over the past week, we have shown that with political will it is possible to agree on a global multibillion-dollar package to recapitalize our banks across many continents. In the next few weeks, we need to show the same resolve and spirit of cooperation to create the rules for our new global economy. If we do this, 2008 will be remembered not just as a year of financial crisis but as the year we started to build the world anew.

Gordon Brown is prime minister of Britain. He wrote this commentary for The Washington Post.