Celebrations to mark the enlargement of the European Union begin this evening and continue over the weekend.
A firework display took place at Sandymount in Dublin, and was described as the most spectacular firework display to be seen in Europe this year. The ten accession states join the EU at midnight.
Ceremonial events attended by EU leaders and celebrations of the culture of the new EU states will take place throughout the weekend.
To facilitate the many events being held over the weekend a number of traffic restrictions and diversions will be put in place.
More than 5,000 gardaí will be on duty in the largest security operation the country has seen in 20 years.
Organisers of May Day protests in Dublin say garda plans have forced them to stage an alternative event in the capital tomorrow.
The Dublin Grassroots Network says planned security measures at Parkgate Street are a recipe for conflict and it is calling on demonstrators to gather at the GPO at 6pm tomorrow evening for a peaceful protest.
Earlier, a group of May Day demonstrators held a protest outside Mountjoy Prison.
Prodi wary over high labour costs
As the EU prepares to celebrate Accession Day, the president of the European Commission has warned that countries with high labour costs could suffer as a result of the expansion.
Romano Prodi has hailed the expansion as a chance for the bloc to finally play an important global role.
But he said countries like Germany and France could lose out because of increased competition for low skilled jobs.
Mr Prodi also warned that the union would be ungovernable if a constitution for an expanded EU was not adopted.
