Sinn Fein leader Gerry Adams has said the decision to accept an invitation for Martin McGuinness to meet the Queen was a "very significant step".
Mr McGuinness is to meet the Queen and shake her hand at a charity reception in Belfast on Wednesday.
Mr Adams said it was about "moving beyond rhetoric to reach out" to unionists as a "gesture of respect".
Mr Adams rejected speculation that Sinn Fein did not want the meeting to be photographed or filmed.
"It is a very significant step and I think it may bring us into a different phase, into a new platform which can be built upon," he told the BBC's Sunday Politics.
"It's good in terms of national reconciliation, it's good in terms of conflict resolution, and while there are still elements here who don't engage in talks and stand back from embracing the peace process, I think it perhaps opens the door to them also."
Sinn Fein agreed to the unprecedented meeting with the Queen following a special meeting of the party in Dublin on Friday.
Mr Adams is to brief party members later on Sunday about the decision to accept the invitation.
DUP MP Jeffrey Donaldson said: "It's perhaps long overdue but nevertheless it is a good thing.
"It's part of the process of moving Northern Ireland forward, that we have respect for our traditions, our cultures and identities.
"This visit is very important to the unionist community, but beyond that, there are many people who will welcome the Queen's visit who are not unionist.
"It's important that Her Majesty feels welcomed in Northern Ireland, it's important that people recognise her position as the head of state and this is progress.
"There will be many victims of IRA terrorism who will find the encounter difficult, but the peace process is about tackling the difficult issues and making the difficult decisions."
Former Northern Ireland First Minister Lord Trimble said the decision to meet the Queen was a natural progression for Sinn Fein.
"The timing's not a surprise; the republicans misjudged the popular reaction to the Queen in the Republic of Ireland during the state visit and I'm sure they wouldn't want to be seen by their electorate as misjudging their reaction to this visit coming up next week," the former UUP leader told Sky News' Murnaghan programme
"So I'm not surprised that it's happening, I'm a little bit surprised at the fuss that they are making about it as if it was a huge deal.
"I'm sure they have known for ages that this was inevitable, and there are still further steps."
Martin McGuinness, a former IRA leader, has been a major figure in the Irish peace process and has been deputy first minister of Northern Ireland for five years.
In the past, Sinn Fein leaders boycotted royal visits to Ireland and the IRA targeted members of the Royal Family.
In 1979, the paramilitary group murdered the Queen's cousin, Lord Mountbatten, while he was on holiday in the Republic of Ireland.
However, following the Queen's highly successful state visit to the Irish Republic last May, there had been mounting speculation that she would meet Sinn Fein.