Fine Gael leader Enda Kenny is attending the summit meeting of the European People's Party (EPP) in Brussels today.
Mr Kenny is representing the Yes campaign at the summit, which is being attended by the EPP heads of government and opposition leaders from the European Union.
Prime Ministers from Germany, France, The Netherlands, Greece, Poland and Sweden are also at the meeting, along with the heads of both the European Commission and European Parliament.
A spokesman for the Fine Gael leader said one of the main agenda items at the summit will be the ratification of the Lisbon Reform Treaty.
"Mr Kenny will be reporting on the situation in Ireland and on Fine Gael's referendum campaign plans," he added.
Mr Kenny will travel to London tomorrow for the city's St Patrick's festivities. He will be accompanied by Clare TD Joe Carey and will also visit a number of centres in the British capital that help and support Irish emigrants in London. Mr Kenny will attend London Mayor Ken Livingston's St Patrick's Festival Ball and return to Ireland on Saturday night.