European Union leaders have said that countries wanting to join will have to meet strict conditions from now on, but that the EU's doors are still open.
Institutional reform will be key for Germany's EU presidency in 2007
Correspondents say the result of the end-of-year summit in Brussels is a subtle hardening of tone towards countries in the membership queue.
The leaders called for reports on the impact of new members on EU policies.
They also said the EU's capacity to absorb new countries would determine the pace of enlargement.
At the same time, the summit resisted calls for any new hurdles to be placed in the path of would-be members.
The leaders also:
- Confirmed a slow-down in talks on Turkey's membership of the EU
- Agreed that EU states must work together on fighting crime - but disagreed on whether to lift the national veto on questions of police and judicial co-operation
- Endorsed plans to increase sea patrols for the purpose of turning back African migrants
- Accused Iran and Syria of destabilising the Middle East
- Expressed deep concern about the deteriorating situation in Darfur
- Endorsed a five-point Middle-East peace initiative
But Mr Barroso suggested that part of the consensus that had emerged on enlargement was that admitting further new members would be dependent on reform of the EU institutions.
However, the UK made clear its rejection of any "automatic" link between institutional reform and the enlargement process.
The summit conclusions, in their final form, said: "To sustain the integration capacity of the EU the acceding countries must be ready and able to fully assume the obligations of Union membership and the Union must be able to function effectively and to develop."
Mr Vanhanen said earlier that the leaders had agreed that EU treaties needed to be reformed, and that they could not "throw out the entire text" of the ill-fated European constitution.
BBC Europe editor Mark Mardell says the summit has set the stage for blazing rows in the future about both enlargement and the constitution.
German Chancellor Angela Merkel said her government would focus on ways to resolve the constitution stalemate during its EU presidency starting on 1 January.
And Spanish Prime Minister Jose Luis Rodriguez Zapatero said he would host a "friends of the constitution" conference in Madrid next month.
The EU leaders also agreed on the basic elements of a comprehensive migration strategy, which they said would feature prominently at an EU-Africa summit in Lisbon in the second half of 2007.
They urged interior ministers and the European Parliament to agree on the creation of the Coastal Patrol network in the first half of the year.