By Oana Lungescu
BBC European regional correspondent
On Sunday, Spain becomes the first country to hold a public referendum on the European Union constitution.
Three of the 25 members have ratified the treaty in parliament. But Spain is the first of more than 10 countries planning to put it to a public vote.
Catalans are fiercely protective of their regional identity
The Spanish government has been pushing the "Yes" vote with campaigns targeting young people and football fans.
But in the north eastern region of Catalonia there is still some indecision.
Twenty years since Spain joined the EU, its economy and infrastructure have grown beyond recognition, pumped up with a net inflow of EU subsidies worth 105bn euros (£96bn).
Some of that money is being put to work in Barcelona, one of busiest and most prosperous ports in the Mediterranean Sea.
By the end of the decade, it will double in size, to capture some of the growing traffic of goods from Asia currently entering Europe through the North Sea.
Joaquim Coello, the president of the port authority, says that one fifth of the money he needs for the expansion will come from the EU. For him, a strong European Union is simply good for business.
"If the EU reinforces its institutions and presence in the world, as well as its internal co-ordination as a common market, that's in our interest from an economic point of view," he says.
Mr Coello is one of very few people in Spain - and in Europe - who have actually read the constitution's 448 articles.
To help the rest make up their mind, the government has distributed five million copies for free. It's also enlisted celebrities, like former football stars Johan Cruyff and Emilio Butragueno, to record radio and television spots.
All the mainstream parties, from the ruling Socialist Party to the opposition conservatives have joined forces in calling for a "Yes" vote.
But Anna Terron, a former socialist member of the European Parliament who now heads a government agency lobbying for Catalan business in Europe, is concerned that too few people might bother to vote.
"People take Europe for granted, so it's difficult to get a political momentum," she says. There may be even less incentive to vote because the referendum will not be binding.
But in regions such as Catalonia, some see it as an opportunity to send a political signal not to Brussels, but to the Spanish government in Madrid.
Catalonia is fiercely protective of its own identity. Outside the cathedral in Barcelona, young and old gather every Sunday to dance the traditional round dance they call the Sardana.
Barcelona is just one part of Spain to have benefited from EU money
One of the young men is wearing a T-shirt saying, "Me, Spanish? I'm Catalan!"
Controversially, those leading the "No" campaign are the Catalan nationalists of Esquerra Republicana (ERC) or Republican Left, a key ally of the ruling socialists.
Although regions like Catalonia already enjoy a large degree of autonomy, with control over culture, education and health, Catalan nationalists want more - a greater voice for what they call "stateless nations" in Europe and official EU status for their languages.
After all, they argue, Catalan is spoken by around 10 million people, more than the population of several new EU member states like Malta, Estonia or Slovakia.
Pilar Dellunde, a regional MP for the Republican Left Party, says Europe should stay true to the motto of the constitution - "United in Diversity."
"We want Catalonia to become an independent state within a federal Europe, so the first step is for our language to be recognised in this treaty," Ms Dellunde says.
For ERC, which militates for independence by peaceful means, a "No" to the European Constitution would in effect be a "No" to Spain but a "Yes" to Europe. This may sound contradictory, but it is true.
In Spain, Eurosceptics are hard to find. Unlike Britain, France or Denmark, where "No" campaigners are warning that the EU Constitution will establish a federal superstate and wipe out national identity, both sides of the argument in Spain say they want more European integration, not less.
This is a view I heard again among students at the university of Barcelona, where all the posters are calling for a vote against the constitution.
Thousands have benefited from EU-sponsored "Erasmus" grants to study abroad and they're not anti-European. But law student Blanca Mestre told me she opposed the EU Constitution because it was too long, too complicated and too remote from ordinary people.
"All my family will vote 'Yes', not because they know what's in it, but because all the media tell us it's a step forward," Blanca explains.
More people speak Catalan than the populations of some EU states
But she is concerned that a "No" vote could be misinterpreted elsewhere in Europe.
"I wouldn't like a totally Eurosceptic No, like in Britain, but I'd be happy with a "No" leading to a better constitution," she says.
Several countries will hold referendums by the end of the year, including Portugal, the Netherlands and France. Others, like Denmark, the Czech Republic and the UK - where the fear of losing national sovereignty is highest - are still to set a date, perhaps waiting to see if someone else says "No" first.
For the first time, this treaty allows member states to leave the EU and many think the UK may have to leave if it ends up as the only country to reject the European constitution.
But if France, one of the engines of the European project, says "Non" this summer, the EU itself would be thrown into turmoil.
It's perhaps an indication of concern that President Jacques Chirac started his campaign in Barcelona, joining the Spanish prime minister in a call for a resounding "Yes" on Sunday.
Like most EU leaders, Mr Chirac is hoping that Spain will set an example for the referendums to come. From this unprecedented exercise in public consultation, the EU could emerge more united in diversity - or more divided than ever.