Around 2,000 delegates have attended the opening day of the European People's Party congress at the Convention Centre in Dublin.
Three people were arrested during an anti-austerity protest which took place outside.
The two-day event is being hosted by Fine Gael, and is being attended by heads of government, party leaders, ministers, national and European parliamentarians, and delegates from EPP member parties across Europe.
The meeting begins the party's campaign for the European Parliament elections and will select its candidate for the president of the European Commission.
The EPP is the largest political party at European level with 12 EU heads of government and 13 members of the European Commission.
Among those attending are German Chancellor Angela Merkel, Spanish Prime Minister Mariano Rajoy, Polish Prime Minister Donald Tusk and Greek Prime Minister Antonis Samaras.
The Presidents of the European Commission and European Council, José Manuel Barroso and Herman Van Rompuy, will also attend.
Minister for European Affairs Paschal Donohoe told RTÉ's Morning Ireland that the crisis in Ukraine will dominate a portion of the conference.
Newly-elected interim Prime Minister of Ukraine Arseny Yatsenyuk, freed opposition leader Yulia Tymoshenko and Vitaly Klitschko are attending.
There were clashes between gardaí and a small number of anti-austerity protesters outside the venue.
It started as around 200 protesters who had marched from Liberty Hall joined a smaller group who had been at the centre for some time.