The leaders of the European Union (EU) are arriving in Washington at a time when relations with the Bush administration are under strain.
EU leaders are worried about US relations
The high-level EU delegation which will meet President Bush on Wednesday includes Greek Prime Minister Costas Simitis, whose country holds the current EU presidency; Romano Prodi, president of the European Commission; and EU foreign policy co-ordinator Javier Solana.
They face a uphill task in rebuilding the transatlantic relationship after the strains of the war against Iraq, which many European governments opposed.
"There is much more to the EU-US relationship than military action in Iraq," a senior EU official said - but there are also many contentious trade issues between the world's two leading economic superpowers.
The EU has moved to defuse some of the issues in relation to terrorism by offering to sign an extradition treaty with the US, and by backing plans for US cargo inspections in EU ports.
On the bigger issue, how far Europe will contribute to costs of reconstruction in Iraq, there are no firm commitments so far.
US officials are hoping for concrete pledges at a donors' conference in September, but they are encouraged that Europe is taking the threat of terrorism seriously.
"What I find encouraging is that the EU does see the threat to freedom in terms compatible with the way the US sees these threats," a senior state department official said.
Europe has agreed extra security measures in the war on terror
The United States is already working closely with the EU in two key trouble spots.
It is collaborating with Europe and the UN to contain Iran's nuclear programme.
And the EU is one of the four parties involved in framing the roadmap for Middle East peace negotiations.
Indeed, the EU foreign affairs commissioner, Mr Solana, wants a tougher, more coherent EU foreign policy which accepts some elements of pre-emption.
But the diversity of views within the EU - which is set to expand to 25 members - makes this difficult to achieve.
On some issues - for example, the jurisdiction of the International Criminal Court - Europe stands united against US objections to such a body standing in judgement over its soldiers.
Meanwhile, both sides have been escalating a series of trade disputes.
The United States is furious that the EU refuses to import any genetically-modified foods, and President Bush has accused Europe of undermining the fight against world hunger by discouraging African states from planting such crops.
The US backs GM crops' potential in developing countries
"None of our member states has tried to impose our views on African or other less developed countries," an EU spokesman said.
US trade representative Robert Zoellick says that French intransigence over reforming the Common Agricultural Policy is holding up hopes of progress in the world trade talks aimed at securing further trade concessions for developing countries.
The EU, however, has a number of trade complaints of its own.
It has recently won a $4bn judgement against the US at the World Trade Organisation over the US tax breaks for exporters.
And it is still smarting over the sanctions over its steel exports imposed one year ago.
The two sides are still struggling to sign an open-skies agreement liberalising air travel between the EU and the US, replacing existing bilateral agreements with individual European countries.
Still, the US and the EU are the world's biggest trading partners, and their companies have invested heavily in each other's economies.
However, the recent fall of the dollar - despite US assertions that it was not intended - has hurt Europe's exporters at a time when their economy is near recession.
There is still a backlash of anti-European feeling in America despite the hopeful official rhetoric.
And the cultural gap between the regions is wider than ever.
Even on terrorism issues, the US finds its hard to understand Europe's reluctance to share computer information on airline passengers, a legacy of strict data protection laws.
And the EU cannot accept that the death penalty is acceptable in criminal terrorism cases - an important issue in the extradition treaty.
For decades, the US and Europe have been the key strategic partners in the world, tied together by a common desire to win the Cold War.
Now the world has changed.
And rebuilding the reality of that link, rather than the rhetoric, will take more than just one summit.