May 1 was the day when 10 new European countries joined the EU.
BBC correspondents across Europe reported on events and the mood among the people of Europe as the EU's political map was transformed.
Tim Franks :: Dublin, Ireland :: 2230GMT
As the European Union's first day as an extended family of 25 draws to a close, the focus must now shift to the workings of the organisation.
There are big issues still to consider - the decision whether to give Turkey a firm date to start negotiations on joining the EU, and most pressingly in just six weeks, the next attempt to reach agreement on a new European constitution.
This has been a hugely important day for Europe, but already the debate about "where next?" and "how?" - those questions are already crowding in.
Mark Simpson :: Dublin, Ireland :: 2210GMT
It's now pretty quiet here and that's because the protesters have been moved back along the road.
Earlier on, about 2100GMT it turned very nasty. The latest figures from the Irish police are that there were 25 people arrested.
There was a female police officer hit by a missile, and taken to hospital and I saw with my own eyes, there was a cameraman hurt.
Kevin Connolly :: Dublin, Ireland :: 2045GMT
The EU enlargement ceremony was conducted inside a huge security cordon involving almost half of the Irish Republic's entire police force.
For much of the day they were left to watch good-naturedly as groups of two or three hundred anarchists and anti-capitalist protesters paraded through the streets in bright sunshine.
In mid-evening though, the mood suddenly changed and several hundred demonstrators were involved in a confrontation with police guarding a gate to Phoenix Park, the venue for today's ceremonies.
It was a surreal standoff in a leafy avenue of detached houses, and at one point a water cannon, borrowed from Northern Ireland's police, was used to contain the crowd.
Adam Easton :: Warsaw, Poland :: 1810GMT
More than 1,000 people have been out on the streets, blowing whistles and waving red balloons, to protest against the EU.
The protest's organisers, a nationalist Catholic Party, compared the rule of Brussels to that of the old Soviet Union.
But they are in a minority.
A survey on the early evening TV news said 56% of Poles were happy to join the EU, with just 29% against.
Rob Cameron :: Prague, Czech Republic :: 1756GMT
The broken champagne bottles have been swept away, and the scenes of jubilation have been replaced by a more sober, reflective atmosphere.
For some, the downsides of accession will be felt almost immediately, such as the widespread VAT increases, which mean Czechs will pay more for a number of goods and services.
But so too will the advantages - no more rude questions from EU immigration officers, no more queues at the border.
In 1989 Czechs cried: "Back to Europe!" Today that call has been answered.
Tamsin Smith :: Nova Gorica, Slovenia :: 1749GMT
I'm at the central train station in Nova Gorica and the party is not over here yet. In fact I'm now listening to the rehearsal for this evenings concert.
There is a feast of roast boar on the menu and lots of local wines and beers.
There is a real sense of occasion here today but not everyone was enthusiastic about new EU membership.
At a café near the local border control one man told me he was a Euro-sceptic, and that he feared that Austrians and Germans who are more wealthy will flock to the area and buy up local property.
Another young man told me he hoped that joining the EU would be something special that would bring something better for him.
Alexandra Fouché :: Brussels, Belgium :: 1740GMT
Celebrations here are coming to an end, and crowds were beginning to leave as the day was set to culminate with the launch of hot air balloons decked with the colours of the EU countries.
They were meant to be inflated, launched and later return for a special night show.
But because the wind was blowing in the wrong direction they will have to stay put, which led some onlookers to wonder aloud whether that boded well for the future of an enlarged EU.
This is the end of a fairly low-key affair here in Brussels, with less time spent on ceremony and more focused on the people.
Nick Thorpe :: Budapest, Hungary :: 1728GMT
The EU accession party in Budapest ended a little earlier than planned. After a day of brilliant sunshine on which hundreds of thousands of revellers celebrated beside the River Danube, the heavens opened in the late afternoon with a spectacular thunderstorm.
Hungary goes into the European Union with high hopes, but many fears as well. There is a sense here that the playing field is by no means even and that the new members are not being treated on an equal basis.
Small businesses and farmers could be hit hardest by competition in the EU, while the large multi-national companies and supermarket chains, which dictate prices, expect bigger profits.
Jon Sopel :: Dublin, Ireland :: 1706GMT
There is a good deal of emotion here now as the national flags of the 25 EU members and the EU flag are raised.
People are hugging each other, there is a real warmth in the hugs and kisses between the leaders as the new members are welcomed and congratulated by the established members.
The leaders I'm sure would love to bottle and carry on with this positive emotion forever, this final moment when the have joined the EU.
They are now off to celebrate in earnest at the home of the Irish President.
William Horsley :: Dublin, Ireland :: 1653GMT
A fanfare opened the ceremony for what is being called one of the most important days in Europe's history.
Young people representing each of the twenty-five member states of the new enlarged European Union presented their national flags, which were raised together with the blue flag with twelve gold stars of the EU.
The Irish president, Mary McAleese, called it a landmark day for the peoples of Europe.
Ireland, a country famous for its friendly ways, has truly laid on a generous and warm welcome for the new members of the union, who extend the EU's territory deep into eastern Europe and the Mediterranean.
Chris Morris :: Warsaw, Poland :: 1639GMT
May Day in Warsaw, the morning Poland joined the European Union and there were more demonstrations on the streets, following the party of the night before.
This time the people on the streets were protesting against the EU and the politicians who led this country back into the political heart of Europe.
The protesters fear a loss of sovereignty. They worry that they culture, their Catholicism could be under threat. It's a nationalist response to an uncertain future. But many Poles are pretty pragmatic about what the EU can offer them.
Mark Simpson :: Dublin, Ireland :: 1632GMT
Outside Government buildings in Dublin's Merrion Sq there is a street party in full swing with loud music belting out across the city.
All the countries have set up their stalls to entice and inform people about their individual nations. The Czech republic stall is handing out holiday brochures and the Estonians are running colouring competitions for the children. But by far the most popular stall and Euro winner is the Cypriot stall which is handing out free white wine.
Tim Franks :: Dublin, Ireland :: 1616GMT
This is a party now of a most elevated nature here in Dublin. All the EU leaders are here now preparing for the flag ceremony and the leaders first family photo with all the new countries represented.
This is one of the events so long in the trailing that it can be anti-climatic in a way. Many of the new countries are dreaming of becoming the next Ireland, achieving economic success.
Angus Roxburgh :: Vilnius, Lithuania :: 1600GMT
It's been 24 hours full of symbolism here in Lithuania. After the fireworks and the concerts came the raising of the European Union flag in front of the presidential palace and the naming of Europe Square in the capital, Vilnius.
This is one of the poorest countries in the EU, but it also has a booming economy - it grew nine percent last year and so people are full of hope that with the help of regional subsidies and the huge tariff-free market, the standard of living will grow rapidly.
There are fears too that Lithuanian farmers and industries will find it hard to compete, but for the moment such worries are far out-weighed by a great sense of history.
Alexandra Fouché :: Brussels, Belgium :: 1540GMT
People have been queuing all day to get in the EU institutions open to the public for the day. These include the European Parliament, the Council of Ministers and the Breydel building, home to the Commission.
Outside the Council of Ministers, they have stopped letting people in. Those who come out seem pleased with their visit, like Embarek Bentouhami, a 48-year old academic from Algeria who has come with his family from Strasbourg, France, for the weekend.
"We saw the enlarged table of ministers big enough for 25, the interpreters' tables, the interpreters' booths. It was all very big, very impressive. What I liked most what the wide array of free drinks on offer - amazing!! We were also given bags-full of EU posters, EU pens, caps, brochures and CDs.
"It is important to bring my children to see this building. For me, it is about peace in the world, unifying people, solidarity between nations.
"Maybe one day Algeria will become part of the EU. It is not in Europe geographically, but economically it is up to joining."
William Horsley :: Dublin, Ireland :: 1530GMT
The leaders of all 25 European Union states, including the ten new members who are joining today, have arrived in Dublin for the formal accession ceremony.
The warm sunshine has added to the upbeat mood, as leaders from Poland and the other central and eastern European states as well as Cyprus and Malta arrived for the first ever family photo of an EU family of 25.
Arguments about the EU constitution and foreign policy are for another day. Here and now the leaders are acting as though they do belong to a family of nations.
Mark Simpson :: Dublin, Ireland :: 1430GMT
There are about 700 anti-globalisation protesters gathered here on Saint Stephen's Green in the centre of Dublin, about to make their way towards the embassy district of the city.
So far it is a colourful, noisy but good-natured protest. It's a stifling hot day here and I think as much as anything the protesters will be going through a test of stamina.
There is a helicopter circling overhead and a huge police presence, which reminds me of home in Northern Ireland, but no indication of any problems.
Alexandra Fouché :: Brussels, Belgium :: 1325GMT
It's getting sunnier and more crowded by the minute here in Brussels.
Crowds have just welcomed 10 Hungarian athletes who have been running all the way from Budapest carrying the 10 flags of the new EU countries.
They left on 15 April and ran some 1,600km. A Hungarian student, Margareta, who came to cheer them on, was all smiles as the runners strolled past to climb onto a large stage dominated by a huge EU flag.
Hungarian runners are welcomed to Brussels
"It's amazing what they did," she says. "I have come here with my friends and we're going to celebrate tonight because Hungary is going back to Europe. It was a big fight to get back in but we won."
William Horsley :: Dublin, Ireland :: 1250GMT
On this very special day for Europe here in Dublin, thousands of ordinary people from across Europe are celebrating at an outdoor fair, while their political leaders trumpet the achievement of bringing eight former communist countries as well as Cyprus and Malta into the EU.
Soon the leaders of all 25 EU states will attend the flag raising ceremony on a sunny day in Dublin's magnificent Phoenix Park and the accession of the ten new countries will be done for all the world to see.
Chris Morris :: Warsaw, Poland :: 1240GMT
As well as the accession celebrations, there is also a rally here against European Union membership.
It has been organised by the League of Polish families, a party which is essentially very nationalist and believes that the EU is going to corrupt polish values. There are polish flags and red and white balloons everywhere at this rally.
Tamsin Smith :: Nova Gorica, Slovenia :: 1222GMT
Until last night the border separating Italy and Slovenia ran through people's gardens, through cemeteries and through the town itself. Although the border still exists there is now a sense of union here.
At the border crossing, just a couple of hundred meters away from me I met some people who were optimistic about joining the EU. They felt there would be small changes that added together would make a difference to their lives here.
But not everyone was happy with this union, one man told me he went to last nights concert for the concert itself and not because he supported Slovenia joining the EU. So there is a mixture of optimism and concern here.
Angus Roxburgh :: Vilnius, Lithuania :: 1215GMT
It's a beautiful afternoon here but it's gone a bit quiet after the noisy celebrations we saw last night. There have been a few symbolic acts today - the EU flag was raised in front of the presidential palace here and a new square was inaugurated - Europe Square.
There's an overwhelming sense of history being made here. The people here are full of optimism - they feel like they may be on the edge of Europe geographically but culturally and politically they feel right in the centre where they belong.
Daniel Boettcher :: Zittau, Germany :: 1211GMT
It was a relatively muted affair here, we had the German Chancellor Gerhard Schroeder with his Polish and Czech counterparts take part in a ceremony at this border crossing.
There are three bridges here, leading from each of the three countries. The political leaders crossed first into Poland, then the Czech Republic and then into Germany. They signed a visitors book in each country.
There was not an overwhelming sense of occasion here. There are celebrations going on, they started yesterday but now the festivities are starting to trail off.
I had one person come up to me and ask me what it was all about today. But most people are optimistic, there were some dissenting voices, one young German dropped his national flag on the ground and said he wouldn't be needing it now.
Some of dignitaries are leaving from here now and I can hear the whirr of helicopters take them off.
Alexandra Fouché :: Brussels, Belgium :: 1152GMT
The main festivities are taking place in the park opposite the commission building in Brussels' EU quarter. There is a collection of stands representing countries and regions from all over Europe. The park is crowded with people keen to sample the food and drink from the new EU countries.
The Czech stand is particularly popular because of its beer. There are also concerts with bands and musicians from the joining EU countries.
Marianne Clayton, an Anglo-French barrister has come with her husband and eight-month-old daughter.
"It would have been inconceivable for me not to take part in the celebrations one way or the other. I am a European, I live in Brussels, the party is nice, family-orientated. It is a bit disappointing that the celebration is not grander, but it is symbolic and that is the main thing," she told me.
Tristana Moore :: Zittau, Germany :: 1140GMT
Celebrations are still going on here. We've just been hearing from the German Chancellor Gerhard Schroeder who is here with his Polish and Czech counterparts. The three men have just been walking across the three different bridges, linking Germany with Poland and the Czech Republic. They then signed three separate golden books and walked along to the stage where each one of them made a speech.
The German Chancellor Gerhard Schroeder spoke about the divisions after the second world war and paid tribute to everyone who has worked together to achieve this common goal of European enlargement. Now the three leaders have left to jet off to Dublin for the ceremony later this afternoon, but the party will be going on here for the rest of the day.
Nick Thorpe :: Budapest, Hungary :: 1050GMT
I'm standing on Freedom Bridge, spanning the Danube in Budapest.
It's a doubly green bridge today - not only is it painted green as normal but the road and tramway in the middle has been turfed for the day.
There are small trees and benches as well and there are crowds of people milling around enjoying the hot spring sunshine.
No one's under any illusions in Hungary that this is a serious day too. For a start, Hungary now has the longest external border of the European Union - more than 1,000km - bordering Croatia, Serbia, Romania and Ukraine.
Hungary's task of guarding that border is also a painful one. There are some 2.5m Hungarians on the other side, living as minorities in those countries. Hungary would like to be a bridge in the future to countries still outside the EU, not a barrier to them.
Tamsin Smith :: Nova Gorica, Slovenia :: 1018GMT
The celebrations are still going on here in the Slovenian border town. May Day is traditionally when workers and trade unionists gather in the main piazza. Today people are marching with EU flags and wearing blue and yellow headscarves.
A short time ago people from both Italy and Slovenia braved the cold to swim together over the river border and later here there will be a European football tournament.
Alexandra Fouche :: Brussels, Belgium :: 0954GMT
People in the European quarter in Brussels were queuing first thing this morning to enter some of the EU institutions open to the public for the day.
People were keen to visit the European institutions
EU balloons were being handed out in front of the commission building to children and their parents.
Streets in the EU quarter have been closed off to make way for a street fair and later on a giant street party.
Hundreds of stands featuring arts and craft as well as food from around the new union will be the main focus of today's celebrations.
Stephen Cviic :: Dublin, Ireland :: 0900GMT
The streets of Dublin are full of colourful flags; other towns and cities are hosting everything from Slovak folk dancing to Hungarian poetry reading, but the main formal events are taking place inside Phoenix Park in Dublin.
There have been fears that protestors from the anti-globalisation movement could try to disrupt proceedings, though most groups have said they'll keep the demonstrations peaceful. Thousands of police and soldiers have been deployed to deal with security.
Tristana Moore :: Zittau, Germany :: 0834GMT
Where I am security is extremely tight. In a couple of hours the Prime Ministers of Poland and Czech Republic and the German Chancellor will meet here at the border of their three countries. They will take a symbolic walk over the bridges behind me here to mark the coming together in the new EU.
There is a lot of enthusiasm for the new union but there are worries too. People in German are worried that Poles and Czechs will come across and take jobs there. The German government have put limits on those from new states who can seek work in this country.
David Eades :: Warsaw, Poland :: 0825GMT
Paul McCartney will be performing here in concert later on Saturday, maintaining that musical theme that began on Friday evening with a rock concert, which lasted for three hours, leading up to the celebrations at midnight.
Just across town in the rather more solemn surroundings of the tomb of the unknown soldier, the flag of the European Union was raised with great respect and with due deference to Poland's new position as a brand new member state, a great moment for the President and the government here as they move into an effectively new era.
Tristana Moore :: Zittau, Germany :: 0753GMT
There were some really emotional scenes here last night in Zittau, as hundreds of Germans, Poles and Czechs got together to celebrate and be reunited.
There is a very positive mood here, on the surface things are very friendly but tensions on issues like farm subsidies lie ahead. Today is a day of celebration, political leaders from all three counties will be here in a show of unity to mark the enlargement later today.
Adam Easton :: Warsaw, Poland :: 0726GMT
Most of the people at the late night party were happy about Poland joining the EU, but many Poles have mixed feelings. They're pragmatic. They're not waking up today expecting a miracle.
They think that prices will go up and their salaries won't, at least for now. There's concern that many small farmers will go out of business, even though they will be among the first people to see tangible benefits from the EU in the shape of direct subsidies.
But Poles voted overwhelmingly to join in a referendum last year. EU membership provides opportunities to study or work abroad and it promises long term prosperity, even if takes quite some time to get there.
Tamsin Smith :: Nova Gorica, Slovenia :: 0717GMT
Slovenia is the only one of the former Yugoslav republics to join the EU. In the light of its turbulent history many people are excited about new opportunities, others here are wondering in the cold light of day, what kind of club they've joined.
Last night many living near the celebrations were frustrated at not being able to enter the events due to high security and chaotic organisation.
One man waiting outside the barrier said that this summed up what he thought about the EU. "Slovenia might now be a member but it doesn't mean that us ordinary people will be allowed to join the party".
Slovenia is one of the smallest new members, with just two million people and it is also the richest. Situated at the gateway to the Balkans, people are asking whether its membership will help bring stability to the region.
Rob Cameron :: Prague, Czech :: 0700GMT
For Czechs, the celebration held last night was all about symbols. At midnight, enormous EU and Czech flags were raised on a granite plinth which once housed a 50-metre high statute of Stalin.
After Stalin's death the communists decided to destroy the statue with dynamite, according to one version of the story his head rolled down the hill and fell into the River Vltava.
Meanwhile the Czech Republic's Eurosceptic - he prefers the term "Eurorealist" - President Vaclav Klaus also delved deep into Czech mythology - at midnight he delivered a live televised speech from the top of a hill called Blanik.
According to legend, Blanik is home to legions of slumbering knights, who will arise only when the Czech nation faces mortal peril. As symbolic gestures go, that one was hard to beat.
Stephen Sackur :: Warsaw, Poland :: 0640GMT
I think this is one of the most spectacular achievements for Europe and the European Union. This is one of the most important events for the EU, it is setting the seal on the recovery of Europe from all the wounds of World War II, from fascism, from the deep division of the cold war. All of that is gone now and we have Europe coming together again, being brought together again.
Helen Fawkes :: Border control post, Ukraine/Poland border :: 0640GMT
I'm inside a border control post on the Ukrainian side of the border. On TV screens in front of me I can see cars and lorries slowly passing through the control post, some have been queuing throughout the night to get into the new EU. Border guards say it is busier than normal.
Millions of euros have been spent on strengthening this border, this is now the front line of Europe's fight against terrorism and organised crime. One of the biggest concerns is illegal immigration. Earlier today six men from India and Pakistan were caught trying to get into Poland and they told me they had paid traffickers thousands of dollars to help them and they were desperate to get into the new EU.
Angus Roxburgh :: Vilnius, Lithuania :: 0625GMT
There was certainly a party here last night and a bit of a hangover this morning. They are brushing up broken glass and debris here in the square beside me outside Vilnius cathedral following last nights concert and celebrations.
There is amazing enthusiasm here for joining the EU, they are hoping for economic prosperity and political stability. no jaded cynicism here. Until 13 years ago they were members of the Soviet Union and for the last decade they have been preparing for this moment, re-joining Europe, where they feel they belong.
Tamsin Smith :: Nova Gorica, Slovenia :: 0610GMT
Here in the town on the border with Italy it is pretty quiet now this morning. There were big celebrations at midnight and until then Nova Gorica was one of Europe's last divided towns, actually split in two between Italy and Slovenia since 1947. So great symbolic importance to hold the ceremonies and celebrations here, there were fireworks, singing, dancing until the small hours despite the rain.
Tim Franks :: Dublin, Ireland :: 0500GMT
Today Europe's political map is transformed. The expansion is certainly ambitious, many of the countries joining are poor. Their political, social and judicial institutions young. They see the promise of Europe wide stability and eventually enrichment. This is a hugely significant day for Europe but it is no where near the end of the story.
Ray Furlong :: Berlin, Germany :: 2330GMT
I'm strolling along Unter den Linden towards the Brandenburg Gate, for decades the symbol of the division of Berlin, Germany and Europe. Now the final line has been drawn under that era. The party so far has been upbeat, with long queues at stalls promoting the cultures of the 10 new member states. But still, this can't be compared with the euphoria that reigned here when the Berlin wall came down.
The majority of Germans are concerned that enlargement will expose them to competition from lower wage, lower tax economies in the East. They are also afraid of a wave of crime - particularly drug smuggling and prostitution. The politicians and media have voiced similar concerns, but at the same time there is not a single significant voice among them against enlargement.
Chris Morris :: Warsaw, Poland :: 2310GMT
Just after midnight here in Warsaw and the president of Poland raised the European Union flag with its gold stars on a blue background. A military band played and there was a huge cheer from the crowd as the fireworks lit up the night sky. Some people held blue and yellow balloons with the words welcome Europe.