In language that represents a breakthrough after years of hairsplitting argument, Nato said the EU could use Nato equipment, personnel and infrastructure to mount operations once the EU itself has made its own arrangements.
Nato leaders "stand ready to define and adopt the necessary arrangements for ready access by the European Union to the collective assets and capabilities of the Alliance, for operations in which the Alliance as a whole is not engaged militarily as an alliance", said the summit communique.
The plans represent a thorough rethink over the past two years of the best ways to allow Europe to play a role on the world stage through both military and political action.
When in government, the Conservatives gave priority to the Western European Union, a body that overlaps both the EU and Nato in terms of membership. Partly for internal party reasons, it shrank from allowing the EU itself to play a role. But Labour has turned towards the EU, and will suggest letting the WEU be partially subsumed within the larger and more established EU.
Britain and France are the only two military powers of any size and effectiveness in the EU, and France is hampered by not being a full member of Nato.
The EU summit in Cologne in June is expected to make more advances that help to turn a European defence policy into a reality after 40 years of abortive arguments.
The plans do not mean that either the European Commission, Parliament or Court of Justice will be engaged in defence policy.
Foreign policy is already run as a separate "pillar" of EU activity, run solely by the governments of member states. Defence is likely to be added as another "pillar", and the insistence of both France and Britain on national control means that the federal institutions will have no role.
The EU will have access to Nato planning capabilities, common assets such as tanker aircraft, electronic warning planes, pipelines and communications, and some forces will eventually be earmarked for use in EU-led operations.
Nato's Deputy Supreme Allied Commander in Europe - traditionally a European post - will have special responsibility for co-ordinating the military side of operations. The post is currently held by General Rupert Smith, a Briton.
America cautiously welcomed the new EU role. "As long as this operation, however it is constituted by the Europeans, operates in co-operation with Nato, I think it will strengthen the capability of the alliance, and I think it will actually help to maintain America's involvement with Nato," said President Bill Clinton.
The shift towards a new European defence policy is just one of a series of reforms in the alliance that had been put in the background by the Kosovo crisis. Nato has also adopted a new Strategic Concept that will allow it to act outside its traditional boundaries. This was a key demand of the US, Nato's main member and paymaster, which wants support for its military activities outside Europe.
Nato will "stand ready, case by case and by consensus ... to contribute to effective conflict prevention and to engage actively in crisis management, including crisis response operations," the new concept says.
This is not quite the commitment to a global Nato some in the US had wanted. It is limited to the "Euro-Atlantic area" - all of Europe plus the former Soviet Union. It means Nato is not going to become involved in the Gulf, for example. And the concept underlines, as France had insisted, that "the United Nations Security Council has the primary responsibility for the maintenance of international peace and security", something the US is wary of.
Three new members - Poland, the Czech Republic and Hungary - joined Nato earlier this year, and more countries will be allowed in eventually, though the details and timing have been left deliberately hazy to avoid antagonising Russia.
A kind of hierarchy has been established of possible new members: Romania and Slovenia, which only just failed to get in last time; Estonia, Latvia and Lithuania, the Baltic republics whose entry is least favoured by Moscow; Bulgaria, which has helped Nato in the Kosovo crisis and boosted its chances; Slovakia; Macedonia; and then Albania. Nato leaders praise Albania for its role in the Balkan crisis but the country is very far from being ready for membership of Nato or the EU.Reuse content