The European constitution was knocked off course when France and the Netherlands rejected it in referendums in May and June 2005, but European leaders are now discussing ways of reviving it in full or in part.
This could mean resurrecting the original text, with minor changes, or drafting a new one.
On the other hand, some countries argue there is no urgent need for institutional reform and that the EU should concentrate instead on policies that deliver immediate practical benefits for citizens.
So far, 16 countries have completed ratification, two of them by referendum; two have very nearly finished ratifying it; and two have rejected it.
That leaves seven countries where the constitution is on ice.
Use this map to find out the state of play in each country.
A legally binding referendum on 29 May 2005 resulted in a "No" vote of almost 55%.
Both the main parties - the governing, conservative UMP and the Socialist Party - were in favour of the constitution, but both parties also had dissidents campaigning for a "No".
The far left and the far right were opposed, as were as were trade unions, some farmers' groups and the anti-globalisation movement.
The two leading candidates running for the French presidency have outlined strategies that could result in French approval for a new treaty. Nicolas Sarkozy favours a slimmed-down treaty that could be adopted by parliamentary vote. Segolene Royal favours sticking to the original constitution, but adding a protocol emphasising the EU's ambitions in social policy. She would then put this to a second referendum.
Some 61.6% of Dutch voters said "No" to the constitution on 1 June 2005, even though the main political parties, trade unions and most newspapers were backing a "Yes".
In January 2006, the then Dutch Foreign Minister Bernard Bot went further than any other European government minister, saying that for the Netherlands, the constitution was "dead". In May 2006 he said he thought the constitution would "stay dead".
However, a new Dutch government formed at the beginning of 2007 has signalled it will co-operate with efforts to tackle institutional reforms in the EU. The government has asked a body known as the State Council to rule on whether a referendum would be necessary on any future treaty based on the constitution.
"The European Constitution will not be offered for
ratification again," a Dutch Cabinet document said in March 2007. "The new treaty must, in content, scope and name, convincingly differ from the European Constitution."
It added: "More co-operation is needed in energy, environment ...
asylum, immigration, anti-terrorism and crime, and foreign
The upper house of the Austrian parliament completed ratification on 25 May 2005. Three members of the far right voted against the constitution, while 59 other representatives approved it.
The lower house voted nearly unanimously in favour of ratification on 11 May.
Some Austrians have voiced fears that the constitution's mutual defence pact would undermine the country's neutrality.
During Austria's EU presidency in 2006, Chancellor Wolfgang Schuessel said that the constitution was not dead, and that Europe was "in the middle of a ratification process".
A vote in the Flemish parliament on 8 February finished the ratification votes by the federal and regional parliaments. The King and the government completed the formalities on 13 June. Foreign Minister Karel de Gucht said on 23 May that an intergovernmental conference should be called in 2008 to revise the EU's fundamental treaties, and that the result should be put to a referendum in 2009.
Bulgaria: The Bulgarian parliament ratified the constitution on 11 May 2005, as part of its preparations for joining the EU on 1 January 2007.
Cyprus' parliament ratified the constitution on 30 June 2005.
The Estonian parliament ratified the constitution on 9 May 2006, in a decision backed by all the country's major political parties.
The Finnish parliament voted to ratify the constitution on 5 December 2006 and this vote has been accepted by President Tarja Halonen.
The Greek parliament ratified the constitution on 19 April 2005, by 268 votes to 17. It had the support of the government and the main opposition party, Pasok.
Hungary's parliament ratified the constitution on 20 December 2004, by a margin of 304 votes to nine.
Italy ratified the constitution on 6 April 2005 with an overwhelming majority in the upper house of parliament - 217 votes to 16. The text, which was signed by EU leaders in Rome in 2004, was approved by the Italian lower house (the Chamber of Deputies) in January 2005. Centrist parties backed the constitution, however, the Northern League and the Communist Party, argued that it eroded regional and national sovereignty.
Prime Minister Romano Prodi told the BBC in March 2007: "Step by step we shall go back in order to have a common basic paper: probably it will be less complete, and maybe in some people's opinion less cumbersome, but it will include all the basic principles, not the specific rules of behaviour."
In February 2007, he and Spanish counterpart Jose Rodriguez Zapatero said they were committed to the "greatest level of integration" provided for in the treaty.
Latvia ratified the EU constitution in parliament on 2 June 2005, by 71 votes to five, just hours after the Dutch had rejected it.
Lithuania became the first country in the EU to ratify the new EU
constitution on 11 November 2004, passing it by 84 votes to four, with three abstentions.
Voters in Luxembourg approved the constitution by 56% in a referendum on 10 July 2005 - held despite agreement on a "pause for reflection" at the EU summit a month earlier, and the postponement of votes in other countries.
The "Yes" campaign had the support of all parliamentary parties. The "No" campaign attracted a varied group of supporters, from left-wing anti-globalisationists to far-right sympathisers. The far-left "di Lenk" party (the Lefties), said the text was too market-orientated and did not do enough for workers. The Luxembourg parliament formally ratified the constitution on 25 October 2005.
Prime Minister Jean-Claude Juncker has expressed the hope that the German EU presidency in the first half of 2007 will make progress with the constitution. But he has also been quoted as predicting that the period of reflection will last until 2009 or 2010.
The Maltese parliament ratified the constitution in a unanimous vote on 6 July 2005.
All three political parties in the country were in favour of ratification. Debate on the constitution focused on the question of whether there is a clash with traditional Maltese Christian values, and possible threats to Maltese sovereignty.
Romania: The Romanian parliament ratified the constitution on 17 May 2005, as part of its preparations for joining the EU on 1 January 2007.
Slovenia's parliament voted overwhelmingly to ratify the European Union constitution on 1 February 2005. MPs supported the move by 79 votes to four.
Spaniards voted for the constitution in a consultative referendum on 20 February 2005 by 77% to 17%. However, turnout was only 42%.
Ratification was completed by votes in the lower house of parliament in April, and in the upper house in May.
All of Spain's main political parties were in favour of the treaty, though there was opposition from regional parties in Catalonia.
Spain hosted a meeting in January 2007 of the 18 Friends of the Constitution - those that have already ratified, or nearly ratified it. Foreign Minister Miguel Angel Moratinos told the meeting the constitution was "a magnificent document" that should be expanded rather than "carved up". On the eve of the meeting, Europe Minister Alberto Navarro said Spain could not accept a "mini-treaty" that dealt with institutional reforms, but scrapped the other parts of the constitution.
Prime Minister Jose Luis Rodriguez Zapatero said in February that the EU needed to find a way to "maintain the essence" of the project, while making it possible for countries that have had problems with ratification to sign up to it.
The German parliament voted to ratify the constitution in May 2005, but the bill has yet to be signed by President Horst Koehler, pending the outcome of a case being heard in the constitutional court. The main political parties are officially in favour of the constitution - which increases Germany's voting power in the Council of Ministers - but the successor of the former East German communist party, the Party of Democratic Socialism, is against it. The constitution also has some opponents on the right.
German Chancellor Angela Merkel has said that cherry-picking bits of the constitution "does not work". She has proposed keeping the text intact, but attaching a declaration on the "social dimension of Europe" to address some of the concerns that led to the rejection of the constitution in France.
"I still support the text we approved in the Bundestag," she told the Suddeutsche Zeitung in May 2006. "All the actions we will undertake in the German EU presidency in 2007 should serve to bring Europe closer to agreeing on the European constitution again."
The Slovak parliament ratified the constitution on 11 May 2005, by 116 votes to 27, with four abstentions. However, a complaint has been made to the constitutional court that the Slovak people should have been given the right to vote on the constitution in a referendum. The Slovak president is unable to complete the ratification process until the court has issued its ruling.
The Czech government says Europe is functioning quite well without a constitution. They say a "bad treaty" would be worse than none at all, though they are not against negotiating a new "basic treaty" from scratch.
Czech President Vaclav Klaus told the BBC in March 2007: "I am absolutely sure that there is no crisis because of the non-existence of the European constitution, but the people who want to accelerate unification process are in a hurry and normal people in Europe are not in a hurry. They can live with the existing structures and rules.
"To pretend the debate is over and it's just a question of bringing in clever speech writers to summarise the completed debate and write a nicer text than the former constitution would be a tragedy, but I am afraid something like that could happen."
Officials said Denmark was "quite pleased" with the original text of the constitution, but the country postponed its planned referendum on the treaty after the French and Dutch "No" votes. Prime Minister Anders Fogh Rasmussen said: "We would like to continue our process, we have prepared everything for the referendum, but of course we cannot put the treaty to a vote in Denmark if there's not a treaty to vote on."
In February 2007, Foreign Minister Per Stig Moeller said Denmark would back German efforts to solve the impasse over the constitution. "If all 27 members vote for it, we will be on board," he said.
Denmark rejected the Maastricht Treaty in 1992 but adopted it in a second vote, after winning opt-outs, in 1993. Danes also voted "No" in a 2000 referendum on acceptance of the euro. It is unclear whether Danish law obliges it to hold a referendum on any new treaty.
The Irish government stopped preparations for a referendum on the constitution after the French and Dutch "No" votes but Irish diplomatic sources say the constitution is a good document, which Ireland would like to see ratified and implemented.
In May 2006, Prime Minister Bertie Ahern confirmed his support for the constitution, describing it as "the right choice for Ireland". He said it would "enable the EU to function more efficiently, more democratically, in a way that is easier to understand".
Irish voters rejected the Nice Treaty in 2001, then approved it in 2002. Ireland is the one country in the EU where the only way of ratifying the constitution, or a successor treaty, is by referendum.
Poland: President Lech Kaczynski has called for a brand new constitution, saying that the original text pushes for more integration than European citizens are willing to accept. He is also quoted as saying it "has practically no chance of being ratified in Poland, neither by referendum
nor by parliamentary vote".
The country's plans for a referendum are on hold.
Prime Minister Jaroslaw Kaczynski has said the EU should abandon the original constitution, and start work on an entirely new Basic Treaty. He and Czech prime minister Mirek Topolanek wrote in a joint letter in February 2007 that it would make more sense for the EU to "create a new basis for co-operation, one that is clearer and involves less red tape".
Portugal will hold a referendum only after a final text has been agreed by all 25 member states. "I don't' believe that the constitutional is dead. Europe needs a constitutional treaty in order to go further. If it's not this exact text, we will have to find something," Prime Minister Jose Socrates said on 9 March 2006.
Sweden: Sweden put ratification on hold after France and the Netherlands rejected the constitution.
The main political parties - conscious that Swedes rejected the euro in 2003 - say a referendum is unnecessary because the constitution does not make fundamental changes to the existing treaties.
United Kingdom: The UK government was preparing to hold a referendum in spring 2006, but shelved these plans after French and Dutch voters rejected the constitution.
Prime Minister Tony Blair told parliament: "Realistically, given the 'No' votes in France and the Netherlands, ratification cannot succeed unless and until those votes change."
Former Foreign Secretary Jack Straw said on 10 January 2006 that the best that could be said about the constitution was that it was "in limbo". He added: "It is difficult to argue that it is not dead." However, Mr Blair said on 2 February 2006: "I accept that we will need to return to the issues around the European constitution. A European Union of 25 cannot function properly with today's rules of governance."
In October 2006, Mr Straw's successor as foreign secretary, Margaret Beckett, commented: "It's a common failing, isn't it? People started to get enthusiastic about a grandiose project but it didn't come off."
The UK last held a referendum on 6 June 1975, two-and-a-half years after joining the European Community, on whether to remain a member. Two-thirds of those who voted said "Yes".