In an historic move, the Queen is to shake hands with Sinn Fein MP and former IRA commander Martin McGuinness.
According to reports by the Press Association, the handshake will take place behind closed doors.
The Queen and Northern Ireland’s deputy first minister will attend a cross-border event in Belfast on Wednesday, which the President of Ireland, Michael D Higgins, will also attend.
Sinn Fein President Gerry Adams said the decision had been taken after consulting with grassroots support and allowing the party’s ruling council, the ard comhairle, to decide at a four-hour meeting in Dublin.
“This will understandably cause difficulties for some republicans and nationalists,” Mr Adams said. “Especially for those folks who suffered at the hands of British forces.”
The ard comhairle decision was not unanimous but was a clear majority, the party confirmed.
Mr McGuinness has said in the past that he would be prepared to meet the Queen if he succeeded in a bid to become president of Ireland.
First Minister Peter Robinson, leader of the Democratic Unionist Party, has said republicans should pay due respect to the Queen as a recognition of her importance to many in Northern Ireland.
Mr McGuinness, who was also in Scotland today at the inter-governmental meeting, has said his party’s decision would be guided on what would be best for the peace process.
Mr Robinson was among those who said such a meeting would also be difficult for the Queen, given that her own family was hurt by republican violence when the IRA killed Lord Mountbatten in a 1979 bombing in Co Sligo.
Former Northern Ireland secretary Peter Hain said: “This is of huge historic importance. It does not mean Sinn Fein have departed one inch from their commitment to an independent Ireland. Nor does it mean the Queen will forget the assassination of her uncle Lord Mountbatten.
“But it does show in shining terms how everybody is turning their backs on the past of horror and violence and moving towards peace between previously bitter enemies.
“Inevitably past victims of IRA atrocities will be upset. Many republicans will see it as a betrayal. But what it shows is that both Martin McGuinness and Her Majesty are saying that the future is much more important than the past. If we get stuck in the past we will never make any progress.”